Roaming between 2.4ghz and 5ghz is usually not a great experience. It's handled by the card and drivers, so YMMV. In my experience, the connection will tend to cling to 2.4ghz due to a perceived higher signal strength (5ghz doesn't travel as far at the same energy levels), then gets stuck on crowded channels with less usable bandwidth from interference.

I set different SSIDs for my current one base station with simultaneous dual band, and pick the appropriate network on each device. I'd likely maintain this strategy even with multiple access points, letting 5ghz clients just roam onto another 5ghz access point, and 2.4 roam to 2.4.