The problem with a non mesh system is that the transition as you move from one part of the house to another usually means a fairly long disconnect. Your device often tries to hold on to the wi-fi it has for too long, and then takes time to handshake with the better one.
Mesh systems do this for you by magic, so it’s a much better experience in practice. My unifi wi-fi devices are all wired to the router, and form a mesh, somehow deciding which access point you should be connected to. Works well.