This is a great place to stay while in Barcelona and I would definitely recommend it. It's easily walkable to a lot of the main attractions, on a relatively quiet street, and a beautiful apartment. We were a group of 6, and the apartment was a perfect size for us.
One thing to be aware of though (and I wish we knew while booking), the host does provide amenities (towels, bath products, pillows, sheets, etc.) but if you need extra or run out of some items, you may have to pay an additional fee. I don't think this is a deal-breaker, but good to know in advance.