It's a great apartment hotel. The room is huge compared to rooms in a hotel. Very modern design and very clean/tidy. There is no daily housekeeping but the apartment we stayed in is for 4 persons, so everything comes in 4, towels, glasses, coffee pods, bath gel, etc. We are only two, so we don't have any problems even when there is no daily housekeeping.
It's very centrally located. Callao subway station right in front on Gran Via, which is probably one of the busiest streets in Madrid, full of people even at 11pm at night. All the shops are within walking distance. (e.g. Primark is 2 streets away. Prado museum is perhaps 15 minutes' walk) Yet, the room is very well insulated, facing a side street. Which means there isn't much of a view if you are on lower floors. (We were on the 6th)
Even without daily housekeeping, there is still a 24-hour concierge and the staff is very friendly and helpful. They gladly provide advice and help us print train tickets etc. Wifi is reasonably fast.
The only slight problem we have is with the shower, the base of which is very shallow, causing water to spill over quite easily onto the bathroom floor. I was thinking about asking the staff for a mop but surprisingly I actually found one right in the storage, so maybe the leaking is actually a well-known problem. :-) All in all, we think it's definitely a great hotel and value-for-money if you can trade off daily housekeeping. We will definitely consider coming back.