Based on what I've seen locally, and read online, the guns may or may not be reliable. They seem to work better with hotter ammo. If you get one that works, good, but some just don't.
Most people who get one that's Ok usually had to search for a brand/type of ammo that particular gun "liked". One man I know went out and bought 50 rounds of every brand and type of .22 ammo available and tested until he found one brand his gun functioned well with. He then bought a 5000 round case of ammo just for it.
If you do buy one, immediately buy an extra magazine or two, if you can find them. Sometimes an unreliable TPH is cured by a different mag.
Since the gun is discontinued, parts are largely unavailable, so if it needs parts or service, you're pretty much SOL.
Get a reliable one that's in good shape and you've got a great gun.