If this is your first time stumbling upon Mainspring then you should be made aware of a recurring theme unique to the contemporary world of micro and independent horology: that of sheer inventiveness and bold creativity unequaled by mainstream brands. Rolex, Omega, Longines, Tissot, Seiko, Citizen…whichever big brand you may think of has nothing on micro/indie brands. Nothing. Because the youngest of houses have no heritage they have to uphold, no stakeholders they have to keep happy, and because there are so many of them which they have to compete with on a daily basis, they must showcase the most daring imagination and creativity in order to stand out from the crowd. And survive. Otherwise they’d never take off or grow sustainably, and the few months or years they were in existence will soon be forgotten. And keep in mind that many of the aforementioned big brands were once microbrands as well, and that many which began post World War II ended during the Quartz Revolution. 

What would be the equivalent of the latter for the myriad of brands currently in existence? No one really knows. 

And here our mission is to tell you about as many outstanding small and young brands as possible, with a few exceptions of course, which is why today I’m happy to be telling you about the Héron Mirabel GMT, the second standalone collection from the Canadian brand. (We previously reviewed the Marinor Ghost North Blue.) The Mirabel GMT is a type of watch the brand describes as a complication dress watch many icons of Swiss horology were known to make a very long while ago. Simply put: elegant timekeeping devices with a complication, for example a vintage Patek Phillippe Perpetual Calendar and not a five-digit Rolex Submariner. (Say what you must about the latter, it isn’t a dress watch.) And the Mirabel GMT definitively belongs to the category of elegant horology and achieves this categorization with a few tricks of its own, which we will soon be discussing. And before we begin, a short PSA: the Mirabel GMT is launching June 5, 2025, at the price of $690 USD. 

Specifications 

So right after mentioning the price of this model, you might get shocked to hear what you get for it by just looking at the spec sheet. (The design is a whole other story.) At the pace at which Héron is going and looking at the incredible value they packed into the Mirabel GMT, I’m starting to wonder if they’re into charitable horology? And this rhetorical question will make sense in a few sentences. Because we’re kicking things off with an enamel dial with applied and polished hour markers, extremely well executed, which we can easily admire thanks to a boxed sapphire crystal complete with inner anti-reflective coating, I did my new pragmatic crystal-quality testing by taping my finger nail on said crystal and it felt as if I was knocking on a 10mm-thick glass table, as the domed sapphire is really thick and is profiled in such a way that it creates lovely vintage-looking distortions at its edges. 

Just as much presence the crystal commands, for the reasons I just mentioned, so does the case for having a sporty stubby profile (which we will get back to later on) and compact dimensions: 37.5mm in diameter, 43.5mm lug-to-lug, 11.8mm thick including the crystal, and a 20mm lug width. The case makes me think of a small hyper-charged sports car with a short wheelbase. Don’t ask me why we watch journalists and bloggers and storytellers—however we see ourselves and you see us—insist on car analogies—because most of us are men?—but that is where the glory of the case stems from. So it is compact and sporty, and it houses a flyer-style GMT caliber, the Miyota 9075 (4Hz/42 hours of power reserve) which is now a standard caliber for micro/indie brands. With a push/pull crown and screw-down crown, the Mirabel GMT comes with a decent 50 meters of water resistance for a complication dress watch. 

The other two pieces of specifications you should be aware of are the strap and Cabochon crown. The former is sourced from Delug*s and made of premium Baranil leather and equipped with quick-release spring-bars. I won’t pretend I knew or that you know about Baranil leather so let me tell you about it: Baranil is a vegetable-tanned calfskin leather made by a French tannery called Degerman which particularity is to be silky-soft to the touch (which I can confirm it is) and to come with a dense and matte finish, which I believe is a superb match for this watch as it does look and feel premium whilst not calling too much attention onto itself (in relation to the dial which has lots of information to display.) And the Cabochon is made of resin and has a semi-translutent finish which I find lovely, and is much more affordable to acquire than the traditional Cartier Cabochon made of sapphire.  

*A Baranil leather strap on Delugs website sells for $110, just to put things in perspective. 

Design 

Do you believe the specs of the Mirabel GMT already tell a great story about this watch? I think they do. And the story they tell is that of great care and attention to detail Héron put into designing and spec’ing their new model. And looking at the dial we can clearly and easily see that it is so from both design and finish perspectives. (But be warned: the watch I reviewed and photographed is a prototype and therefore comes with a couple of imperfections, mainly a few slanted numerals.) Our discovery of the dial then shall begin with the handset, polished Alpha hands the particularities of which are their lance-like shape and facets, meaning they gloriously reflect light in all directions which do not preclude them from being highly legible at most angles. They are completed and complemented by a capped and polished needle seconds hand and a partially polished GMT hand which tip makes me think of a dart. Whatever it is shaped after, it looks great. 

Then the dial of the Mirabel GMT has a sector layout, where the central section is endowed with a matte finish and crossing hairlines, which are connected to a first circle which leads to a second one, together framing and forming the base of the dial. The next sector encompasses the polished and applied hour markers which sit on a portion that received a subtle sunburst effect, which in even more subtle ways play with the markers, where the light reflected by the former accompanies the light reflected by the latter in equal measures. Further out we find a narrow railroad minute track where the segments marking the 1-hour or 5-minute increments are thicker, and beyond an unframed GMT scale where the even hours are indicated by Arabic numerals printed in an old-school serif typeface and the odd hours are indicated with dots. The dial is endowed with superb proportions where all of its elements seamlessly cohabit with one another. A true work of art. 

And don’t get me started on the case which is my favorite part of the Mirabel GMT’s design. As mentioned earlier, I find it to have a sporty stubby profile, meaning it’s dense and slightly aggressive, a sensation which is accentuated by the predominance of polished accents on the fixed bezel, upper sections of the case including the chamfers, outer parts of the lugs, as well as two additional chamfers located at the bottom part of the case and lodged between the lugs. Héron describes the case as a vintage-inspired C-Case, and once again I won’t pretend I knew or that you know about C-shaped cases (and if you do then please forgive my own ignorance): they were designed for Omega in 1964 by the legendary Gerald Genta for the third iteration of the  Constellation. Héron beefed it up, flanked it with a diamond-shaped crown at the three, and the result is pure vintage horological goodness. The Mirabel GMT is therefore a complete visual package. 

The Heart of the Matter

I actually have two more things to say about the case before we move onto the heart of the matter. First is the perfect arching of the mid-case + lug combo which looks elegant and delicate and aids in making the watch appear thinner on the wrist. Second is how much attention Héron put into designing the case-back: it has a 24-hour scale surrounded by a Worldtimer complication (if that’s how we can call it when it's engraved on a case-back,) as well as two hand-painted semi circles made of enamel representing the AM hours in black and PM hours in white. I generally don’t care what a case-back of a watch looks like because—hey–I don’t see it, but here it’s cool and clever. So this leads us into the typical thought-provoking conclusion of my lengthy reviews (snore) which today are as follows: 

(1) the Mirabel GMT is exquisitely designed and made, a statement I feel comfortable making despite the few imperfections of the prototype: (2) it is too cheap to purchase for what you get. Whilst, between you and me, the Marinor Ghost North Blue did intrigue me for it was a paired-down and minimalist version of a traditional diver, it didn’t translate into a refinement of design and manufacturing as much as the new Mirabel does. The former was a cool interpretation of a dive watch while the latter is much more than that—a new concept, or perhaps a revisited one, made anew by two young watch entrepreneurs who have nothing to lose but everything to gain by being bold and peaking at a style of watch few brands dare looking at. Because the Mirabel GMT is indeed two things: a complication dress watch as the brand puts it, and a mature second opus. 

Conclusion 

Nowadays you can stretch your money to unimaginable extents thanks to the hard work and dedication of micro/independent brands. Five years ago $700 USD got you a so-called high quality homage of a Rolex Submariner with a basic (but nonetheless reliable) Seiko NH35A caliber, a folder-over clasp, micro-adjustment holes, and a printed dial. Today you get a flyer GMT caliber, a finely manufactured and finished case, a thick piece of sapphire, and complex and multi-textured dials for the same amount of money which again begs the question as to what kind of business is Héron into? Because even though in 2025 you typically get more for your money, there is still a limit as to what you indeed receive. $690 USD for the Héron Mirabel GMT is excellent value, and should you be moved by its design, then you also get a refined and classically styled design. 

Please do take a moment to check out the brand’s website and don’t miss the launch on June 5, 2025. 

Thanks for reading.