I'm going to add to @Ryan_Miles answer - roaming works fine for a good bug free client.
Lets say you have a really new device with WiFi-6E support. Will its software handle roaming to an MR36 using WiFi-6, or will it hold onto the WiFi-6E connection because it can't see anything else using the same band, until it can no longer hold on, and then roam?
You lower your risk of exposing client roaming issues (with the client) by sticking to the same model APs
.
Clients are you biggest risk. The different model APs will happily handle the roaming request though.