Helena's place was exactly like it was described in the AirBNB listing. We loved the place and would stay here again in a NY minute.
Pros - Location, just outside of Plaza Mayor. A central location in city like Madrid is necessary. Very clean, even the balcony/terrace had been well cleaned when we arrived. Wifi was strong and consistent. Hot water was plentiful. Heat was perfect and quiet. Washing machine worked well and the drying rack is large enough to handle everything. Kitchen, while small, had everything you need and plenty of extras. Check-in was very smooth. Helena sent a video showing how everything worked and where everything was. It was very helpful. The apartment was large, with the main bedroom and living area both being much larger than I thought they would be. The balcony was perfect. A great place to relax and the end of the evening and share the stories of the day. The decorations and finishing touches of the place made you feel at home immediately. Elevator worked without an issue.
Cons - I'm having a hard time coming up with any. The door to the balcony was small (even though the balcony was a great size). We prefer minimalist decor and this place was decorated in a charming and very personal way. Not a negative, I guess, just not our style (even though we knew this from the pictures).
Additional Comments - We used the stairs the entire time (except to transport luggage up and down) as this is just what we do. Make sure you turn on the lights to the stairwell when you get in as the stairwell can get pretty dark. The main door to the place can be locked from the outside locking the person inside. We experienced this as when the lock is engaged from the outside, the dead bolt couldn't be undone from the inside. This caused us a slight hiccup, but was no big deal. However, you should be aware as this could be an issue. There may be a way to undo this, but we couldn't figure it out. We did NOT ask Helena, so there may very well be a simple solution to this.
To summarize, if you are going to Madrid, stay at Helena's.