"1) On a slope, the luggage is likely to roll by itself (this happened in our driveway)."

That's probably the biggest disadvantage, in my mind. One of my colleagues travel with it once and it seemed quite convenient, until she put the spinner luggage in the baggage area of a shuttle and mention that it may roll towards us.

Other than that, it seems like an okay, normal luggage. I don't quite see the appeal, but to each his/her own.