I have two Ubiquiti AP-AC Pro APs, and I've been running OpenWRT just fine on them for the past year and a half. Completely rock solid. I didn't do performance testing with the stock firmware, so I don't know if I get the same WiFi speeds, but what I do get is more than sufficient for my purposes.

Maybe other hardware doesn't work as well, but I think if you choose carefully, it's fine.