3 points
I don’t think there’s a way of checking how many games are like this, but I find that the majority of games I’ve tried doing that just work, and the ones that don’t are mostly bad programming (e.g. crashes trying to load the steam library).
That’s GOG’s whole schtick, none of the games they sell have DRM when purchased from their store. You can always copy the installer to another computer and run it.
That’s not entirely true, as a general rule I think GoG has a lot less DRM-ed games, but it’s not 100% DRM free like they sometimes claim https://www.gog.com/forum/general/drm_on_gog_list_of_singleplayer_games_with_drm/page1