The output of a home concentrator runs about 98% O2 ... it's not as good as bottled gas or LOX, but it's good enough. The medical supply company doesn't have to deliver bottles every week, so it's cheaper. If the patient isn't very mobile, it can be the better choice. Some of the concentrator systems include a device to fill high-pressure bottles for use when the patient goes out of the house.
Also, FWIW, some military aviation units use a concentrator to fill the aircraft supplemental oxygen system. I work with a unit that has such a device.