We didn't meet, but communicating was fast and easy. Check-In and -out was no problem at all.
The location is very good. The metro is around 5 minutes away. But many places in the centrum can be reached by walking which is nice because this way you can explore and discover a lot.
The flat itself was comfortable and big enough for two people. There are many interesting details everywhere (I still have no idea what that big metal bazooka-like thing is, probably a very old type of flashlight haha). It was very hot in Madrid, but the flat has an air conditioner and a fan which was great. And it was a pretty quiet place.
Definitely recommendable!