It's a little odd to say it has a proprietary OS "rather than SteamOS or Windows." You might expect either of those for a handheld PC but this is a cheap handheld that runs one emulator. Either Android or some light Linux distro like the Chinese emulator handhelds in its price range would be the alternative to something custom.
MyArcade is preparing to launch the Atari GameStation Portable, a 7-inch gaming handheld designed to play over 200 classic Atari games. To that end, the GameStation Portable has an Atari Trak ball, paddle and a keypad, among other features.