I've seen them in my local sex shop, first I thought they were some kind of weird pouch erm...They look rather crap, and the shopkeeper said they can hardly sell them. So maybe that reflects on their actual quality.
It is useless unless you work yourself up hard enough to enter it. It does envelop you (like a pvssy) but masturbation works differently. You need the rapid changes in speed and contacts to get off, counteracting the exertion and effort of doing it. A fleshlight "plays only one note". I also found that I had to finish with my hand, particularly the "milking" action at the end.