I'd personally vote against the TRP Spyre/Spyke solely because fiddling around with a hex key* to manually adjust for pad wear every few weeks (on both sides, of course) is such a massive pita. It drove me nuts; and it becomes so much worse when you have a bike with actual decent brakes (= hydros) at the same time to compare to.
Where fully hydraulic is not an option, I'd either research those cable to hydro converter thingies (no clue if there is a decent one you can actually buy or if that went nowhere) or try a hybrid caliper (still manual pad wear adjustment, but way less painful) or maybe, just maybe, research other mechanical options (but I didn't like my Avid BBs either).
It being flatmount (vs having to use an adapter) would be the very very lowest of my priorities.
* For clarification: I do know barrel adjusters, but they can only do so much. Also, the brake really starts to feel a little different, if you try to utilise the whole motion range of the swing arm for adjustment - but it's still nowhere near enough to get through a full pad.