I moved my four HAP AC devices onto OpenWRT; speed and stability has been much improved, and roaming works much better. If you don't need WiFi 6 then I'd go as far as to say this is a great solution.
That has been my (one?) major complaint with my Ubiquiti APs - I have four of them scattered around my house/garage and moving between them always suffers a bit of a delay in handing over (or refusing to hand over at all).
I recently migrated a router (not Ubiquiti) over to OpenWRT and have been happy with the stability. I read a bit about roaming, but thought it looked a little daunting.
Here's an example: https://parkercs.tech/enabling-802-11r-fast-roaming-transiti...
I did lose the central management interface of Mikrotik (CAPsMAN) but for my home set-up this wasn't a big deal. I used the backup and restore capability in OpenWRT's LUCI interface to clone most of the settings.
Roaming / fast transition now works much better. I do still lose a few packets as I wonder around but nowhere near as flakey as on the Mikrotik stack.
I did spend an inordinate amount of time optimising channels, signal strength and placement etc. on the Mikrotik stack before migrating over, and so I kept these settings on OpenWRT. I think a lot of making wifi work well is in this particular black art. All things being equal, though, OpenWRT works better for me.
for home use at this point I would also recommend mikrotik routers over anything ubiquiti edgeOS based, since they seem to have abandoned development on their fork of vyatta... the $50 edgerouter-x (ER-X) as a standalone wired gigabit router was a good choice in 2017 but not so much anymore.