If you have all five episodes, you can order the DVD for free + shipping. Since the DVD is only available through them (i.e. is not in retail), it's entirely lacking in DRM. Installation and gameplay were perfect.
Just make sure to have the following:
- Direct X
- MS VC++ 2005 redist. runtime
- MS VC++ 2008 redist. runtime
I used to think having both MSVC 2005 and 2008 was redundant, but certain 2008 functions call on 2005 functions. Funny thing is, the downloadable versions do not need 2005, but the DVD does.
Edit: It's possible that only 2005 is necessary.