Collin's place is a great option for small groups! The apartment is clean, secure, quiet, and in a great location. It's also fairly spacious for SF standards. The Harry Potter touches are an entertaining feature for fans of the series, but the place would still be charming for muggles...
As a host, Collin is incredibly responsive and available via Airbnb messenger at a moment's notice. I wouldn't hesitate to stay here again. In fact, we were already talking about returning when the Cursed Child play comes to SF. It was a perfect fit for our group of three coming into the city for a concert at The Masonic (to note, the apartment is *right* down the street from the Bill Graham Civic Auditorium and would an ideal place to stay if in town for a concert/event there).
The only thing to note is that the bathroom (which is spacious and clean) is attached to one of the bedrooms. Meaning you must walk through the bedroom to enter the bathroom. Not at all an issue for our group, but could be odd/awkward depending on your fellow travel companions.