Pin valved or On/Off, they work fine and make for a better balanced rifle.
This one has had it's barrel shortened, and while it could use 9oz. bottles, the 3.5's have been working out a lot better for me.

Are still a few hard-core pump paintball players, and these tanks are popular with them, which is why of all the old-school type tanks, the 3.5's are still being made.