I stayed at Alvaro's place for almost four months and it was perfect for one person (or maybe two). The place itself was very clean and modern. As for the location, it's unbeatable and close to two metro stops: Anton Martin and Lavapies.
The bed was comfy and suitable for one person, for two people it may have been a bit small but I slept on the couch many times and trust me, it's just as comfortable!
Overall, I recommend the flat for a short term stay or a long term stay. The stairs are killer, so if you're staying for a week or more and have difficulty moving, I would recommend a place with an elevator as its on the very top floor.
It also has a wonderful rooftop as well, which I enjoyed greatly.
Overall, a 5/5 experience from me.