Slick move with the Pro Mini and the 90 degree FTDI breakout. FX-SaberOS has always been compatible with the Pro Mini but I never see anyone use them.
Well, you know what they say, Cram-fu is the mother of invention. The extra 3.7mm saved by not having a Micro USB is worth the hassle of dealing with the Pro Mini.
That said, I'm only really still using them because I had a custom carrier board made for my saber commission last year, in an attempt to make it look like a professional install job, and the PCB place I went to had a minimum order of 3. One spare down, one to go!
Honestly, they're not ideal for the job. I mean, they've got the hardware requirements to run FX-SaberOS (trying S.T.R.E.A.M. on it is on my to-do list for the weekend) but the fact that they've been officially discontinued by Arduino in favour of the Pro Micro means that only the Chinese knockoff manufacturers make them these days.
Quality, and more importantly, pin locations, vary wildly between manufacturer. I've seen clones with the official Arduino pinout, some with the DF-Robot pinout, some a mirrored DF-robot, some entirely random, etc. I did toy with the idea of offering the carrier board I designed to Brewboard/Saber Republic as an alternative DIYino carrier, but the lack of consistency between Pro mini pinouts is what nipped that idea in the bud.
And to top that, as happened on my first pro mini order, eBay/Amazon sellers will just happily mix up the 3.3V, 8MHz version with the 5V, 16MHz version. Because hey, a Pro mini is a Pro mini, right?
I mean, at least with the Nano clones, pinout, voltage and clock speed will be consistent. I still wish there was one without the bulky USB connection. The Pro micro is a step in the right direction, but its pinout is a mess that would require reworking the stock FXS-OS pins. Or the end user modifying the code themselves.
...huh, that turned into a rant real quick.