>>QuiEgo+XK1
While Unifi supports wireless backhaul/mesh, the entire system is heavily designed to encourage wired backhaul - all their wireless APs are PoE for a reason. If you are going to invest in the Unifi ecosystem, it makes sense to invest in decent networking - wireless "mesh" is always a compromise for running multiple wireless APs.
If you are in a situation you need multiple wireless APs but can't run ethernet to them (like renting etc), I'd probably pass on a Unifi system personally.