In reply to steve taylor:
I've got 6 mesh units set up to extend one network and my experience is that it's patchy. Like, individual units lose connection or just randomly drop out pretty frequently (and they are definitely not too far from one another), sometimes needing to be power cycled to get the connection back and if you want to extend even a pretty small distance, you will find yourself having to place 2 or 3 of them in line, at which point you double or triple the number of times your connection drops out because one unit or another is having a paddy. I can't comment on whether you can get better results by hard-wiring them with ethernet cable - that might create a more reliable network.
Mine are TP-link Deco units. M5 and M4.
(also the M5s run pretty hot so it's worth putting them somewhere with good air movement and not next to anything particularly flammable).