I’ve got a TP Link Extender, which I got for the summer house. You set it up as the same network with .ext on the end – same password etc. With my normal router being quite close to the outside wall facing the garden, I couldn’t find a place to site the extender to sufficiently improve the wi-fi in the summer house. I’ve actually got the extender in the summer house now, as I can get a wi-fi signal in there (just). It does seem to throttle speed though, even though it claims to have very good speed capability.
I’ve since put a TP powerline that I had kicking about (note, these are 2 different types of devices) in the summer house. Despite claims that you have to be on the same circuit – i.e. base device and remote device on the same ring main for example, it’s working fine at almost full speed. The base is on the downstairs ring and the shed is powered on a separate sub-main direct from the consumer unit via an armoured cable