Question about UniFi AP AC-PRO - 25509

Roaming is supported, also for VoIP theoretically at least (zero handoff: help.ubnt.com/hc/en-us/articles/205144590-UniFi-What-is-Zero...). However, it should be the same L3 network, otherwise there are problems because the devices do not know that they have to obtain a new or different IP.

Roaming works with the same SSID on an L2 network, at least I have not noticed any significant interruptions during tests. However, I have not tested whether a VoIP or video call is interrupted.

The UniFi APs are designed to operate in offices and schools. In these environments, it is common for all APs to have the same SSID. I can't test it myself at the moment because we only have one AP in operation, but I strongly assume that it works.
According to the description on the website, the APs even set themselves up so that they interfere with each other as little as possible.