I was visiting for a work event nearby. The apartment is quite tiny (there were two of us) but is super well designed in a Japanese type style, so you have everything you need. The bed is fabulously comfortable and the place was nice and clean.
Re location, it's close to shops as well as to the 34 bus which takes you directly to Atocha station or the Prado, and there's also the metro nearby.
Underfloor heating works beautifully, so it's cosy in winter. (You just need to remember not to have both upstairs and downstairs turned on at once to avoid fuse blowing.)
Rafa and Luis replied to messages almost instantly. Great hosts.