Mar's place has an awesome location, very close to the many points of interest but at the same time it is not a very busy area. We had a family stay with around 10 relative, and there was enough space for everybody including the kids.
The host was always available and had a fast response. In the case you need to bring your car rental, there is a public parking just couple of blocks away. we were worried about it since we knew Downtown Madrid had many restrictions for parking, but as long as your car has the eco sticker from the City you can park at those public parkings that are very affordable .
I highly recommend Mar's place, and will consider to return at some point. :)