mobutu: Haha, turns out I already gog-bought it sometime ago :)
Now play it, it seems quite a good game (the little I have played it :)).
I usually don't try to gather several digital copies of the same game (as long as one of them is an up-to-date DRM-free version), but it so happens I have at least four digital copies of this game:
1. Originally bought it from Frictional Games' homepage directly.
2. At some point got it also on GOG, probably part of some bundle.
3. Also have the Humble Bundle version.
4. Steam-version from the aforementioned Humble Bundle.
GOG version is the one I've installed and played though.