We stayed in Marc's apartment for 5 days in August and it was the first time we had been to Barcelona. Marc and his wife made us feel very welcome.
The apartment was spotless and although it is small and basic, had everything we needed for our trip including wifi which was really helpful. There are a lot of stairs to the apartment and so I wouldn't recommend it to anyone who struggles in this regard but it was no problem for us. The apartment is in a great area, Sant Antoni which is just a ten minute walk from Las Ramblas. Sant Antoni itself has some great bars and cafés which are only a short walk from the apartment. The San Antoni metro is only a 5 minute walk away and Poble Sec is about 10 minutes away so great access to the rest of the city. Marc and his wife responded promptly whenever we needed to speak to them - we had no issues during our stay but I have no doubt that they would have been more than attentive if we did. All in all the apartment made a great base for our trip to Barcelona and I would certainly recommend it to anyone who plans on visiting the city.