I went to Barcelona on a birthday trip for a few days with three other friends, and I can say we had a good time there.
The location of the flat was absolutely perfect: one minute away from Sagrada Familia, and minutes away to all major sight seeing spots in Barcelona. We had everything we needed right next to it: the tube station, a supermarket and a café where we could get our coffees in the morning.
The flat itself was nice and comfortable, and we enjoyed it. One thing that we did notice was that it was considerably smaller and darker than it was in the photos advertised, so I must say we were slightly disappointed by that. Plus, the TV was still not working even if I saw a comment about it being broken from quite some time ago. But in the end, we only used the flat to sleep for a couple of hours at night, so it wasn't that big of an inconvenience eventually.
Leo was very prompt in replying to all my messages and Kate helped us as well when we asked her for a few things to make our stay more comfortable.
All in all, it was a pleasant mini holiday and I'd recommend the flat to anybody who is looking for an ultra central place to stay in Barcelona.