Okay, so I finally caved and bought the Bar Fly 4 TT mount after weeks of debating whether a chunk of plastic was worth $32. Spoiler: It kinda is... but also kinda isn't?
First off, the compatibility is LEGIT. My Garmin 945 sits perfectly between my aerobars now instead of hiding on the stem like some shy kid at a school dance. And yes, it holds my GoPro too (though more on that later).
The installation was stupid easy - just clamp it on with the included rubber protector (no scratches!). Though fair warning: if you're using Garmin's quick release mount, prepare for some forceful clicking action. Mine still doesn't snap in as satisfyingly as the original mount.
Now for the gripes: That GoPro mount placement? Whoever designed it must've never actually used a GoPro. You need an Allen key to attach/detach because they put the screw on the aerobar side. Why not use thumb screws? WHY?! Also saw reviews about the hinge breaking when torqued - mine's holding up so far, but I'm babying it.
At the end of the day, this is basically your only option for 24mm bars (looking at you, Deda Elementi owners). It does its job well despite some questionable design choices. Just don't think too hard about paying premium price for fancy plastic.