Basically a great place to stay! It is a big apartment at the heart of Madrid. The host is responsive to problems and they get sorted.
A few caveats though that we learnt over 2 weeks staying there:
It is on a side street with a set of bars and restaurants. This means it is noisy in the night and this was even with the 11pm curfew in place.
The flat is north facing so you never get direct sunlight. This may be perfect in high summer but for us in April it meant it was too cold to really enjoy the light flat with all the open windows etc.
It is a commercial feeling air BnB experience. So you have to pay for it extras like someone to do your washing or do a late checkout. It is basically more like an apartment hotel.
All round though I repeat that this is a great place to stay and we thoroughly enjoyed being there!