We stayed in Duermo for 3 nights and really enjoyed our stay!
The staff is very welcoming, our room was clean and simple, with a very nice view. The free breakfast and wifi connection were also very appreciated.
There is a metro station and a shop open 24h a day in the same street.
There are only 2 shared bathrooms, but we never had to wait for more than a few minutes.
It's by far my best experience in a inexpensive hotel and I would definitely come back if I had to stay in Madrid again!