I played one of those today at the mall. The joystick feels a bit strange, it favors the diagonals (unlike the original Nes stick that favored the primary directions).
The "original" arcade versions are the nes ports. Galaga seemed a bit jerky though, not as smooth as on a real Nes. It has a cartridge slot in the back. I asked the lady selling them if Nes cartridges worked in it and she said "No, that is for the expansion cartridge that we have coming out around Easter". I then asked her if she worked for the bootleg Taiwan factory that put these out, and then she sort of started helping someone else instead.