We had a fantastic time. They were very helpful, supplied us with a baby bed with no extra charge and assisted with anything we needed. The apartment is located smack at the center of the city, walking distance from most main attractions and spitting distance from bakeries, delis, supermarkets, restaurants, and the famous San Gines chocolateria.
Staying here is getting the best of both worlds. It's an Airbnb apartment, not a big fat hotel, but you do have a reception for most of the day time to help you with anything you need, plus you get some nice extras like a free bottle of water waiting in the apartment, along with free tea, Nespresso capsules and Lotus cookies.
The living room, kitchen and dining area are spacious and were perfect for us (we were 6 + a toddler) to hang around and have breakfast. It was even large enough for the energetic toddler to run around in.
Two of the three room have a balcony (living room has two as well) which is great, but also can be noisy as the apartment is facing the main street (Calle Mayor). The third room has it's bathtub and toilet and has no windows or balconies. So it's quieter but also smaller and basically only good for sleeping.
Great choice for a group visiting Madrid for the first time.