TL;DR Good deal if you are low on budget and need a place to stay for 4-6 people.
We've stayed just one night at Luca's apartment, it was a good experience overall. Luca is very hospitable, he was waiting for us near the building when we were checking-in.
The apartment is good but feels worn out. Double rooms are bright and have very nice balconies. Single rooms are small and don't have windows. The kitchen is pretty basic but ok for simple cooking meals or making tea. The bathroom had no lock on the door, which provoke confusing situations if you are more than 2 people, I hope Luca will fix it. A boiler can't warm up water fast enough to take a shower as long as you want: Luca recommends to take a shower not longer than 5 minutes per person.
The location is also good in terms of proximity to the main places of attraction: 15 minutes from Plaça d'Espanya, 20 minutes from the Gothic Quarter, 30 minutes from Barceloneta and Barcelona Sants by foot. Very close to a metro station.