I've tried the generic wi-fi extenders before and had issues with devices sticking with the weaker wi-fi rather than being passed on to the stronger connection. I was hoping a system using the Ubiquiti APs exclusively may deal with this better.
I hadn't considered power-line adapters plugged into the AP. I have used them in the past and they weren't great (old electrics) but the technology may have moved on. I also had the very weird issue that I was initially connecting to a network 2 doors down (I knew this because I could access their NAS and see documents stored on there) which made me somewhat wary of them.
Maybe I'll give them another try and see, I've had a new consumer unit fitted since last time I tried which may make a difference.