Took out the M4 yesterday and blasted a few rounds with the Korean "beta" mag. ZERO malfunctions. Even the cheap a$$ loader worked just fine. For a range toy, I say "go for it". YMMV.
Stupid me forgot to take the Galil out too though. So I don't know how well it'll work with the AR magwell. It fits, but I don't want to assume that it will feed properly until I actually shoot it.
So go ahead and get a couple there 4th, as long as you're not planning to take them to Trashcanistan for actual combat.