Is there a DRM free version available for purchase?

[Your Computer]

It has to be restricted otherwise every TPB copy would be considered legal after entering a specific cd key. It's not forced like Steam but I think it has the usual one user legal restrictions.

It may not be legal, but there's nothing, as far i can tell, that prevents the same serial key from working for multiple users. In the case of Steam, even though a serial key is not required, the Steam application and its DRM policies are what decides whether or not you can play the game.