2 will cover my needs. Do they actually work like a mesh? As in use backhaul radio to communicate between them and allow seamless switch from one to another as you travel around your home?
Yes, this model supports Wireless Uplink with Plug & Play Mesh:
> Wireless Uplink functionality enables wireless connectivity between APs for extended range. One wired UniFi AP uplink supports up to four wireless downlinks on a single operating band, allowing wireless adoption of devices in their default state and real-time changes to network topology. For devices that support Plug & Play Mesh, this functionality is extended to allow multi-hop wireless uplink – so wirelessly uplinked APs can support uplink to other wirelessly uplinked APs.
(quote is from the datasheet PDF)
[0] https://store.ui.com/products/unifi-ac-mesh-pro-ap