I’m looking at putting mine up in the ceiling but am debating if I add a second one at the other end of the house or not. As it is it already covers the whole house but I’m getting 35MB/s transfer rates at the front and 2.5MB/s at the back with my 2013 rMBP.
The front of house is where I am 99% of the time (and the kids are at the back) so this works for me and while I could trade off a little speed and improve the back performance I’m tempted to just add a second one out back for speed everywhere!
That said when it goes up in the roof space it will likely change the coverage a little so I might just wait and see what happens (although I’ll probably get two cables installed in the roof space at the same time since pulling 1/2 into that space will be virtually the same cost).