I've owned, managed, and worked at a lot of FBO's. O2 was always a money losing hassle. Even if you charge $50 or more you lose time and money. It's actually a courtesy service. That said I've always looked at hard mount systems in small planes as being dumb honestly. Harder to repair, heavy, often leaky, and I've seen wear/tear and damage just from them being serviced. Just another way for everyone to lose time and money. Go portable and get filled at medical or welding supply places when you can. If you need a fill at an FBO just pull the bottle and hand it to them. Better for everyone.