I had the opportunity to spend a short stay (~1.5 weeks) at this location and would recommend it. Due to the size of the space, it is best suited to solo adventures or one couple.
Communication with Stefanie and Joan was fantastic. They go out of their way to ensure you have all the information you might need for your stay (restaurant and site recommendations, clear instructions for use of the amenities, etc.). The space itself is well-equipped so if you enjoy preparing your own meals, you have access to any cooking utensils you need.
For location, this space simply cannot be beat. It is within walking distance of everything (tourist sites, supermarkets, restaurants, public transportation, etc.).
An item of note if you are sensitive to noise is that Barcelona is a lively city and El Raval is no exception; there is likely to be intermittent noise at varying times of the day and night during your stay. Stefanie and Joan note this in the description (I mention it only as a reminder).