JUST TAKE NOTE that GMG does not have a gift option!!!!
meaning: if you buy a game once on GMG you can never ever buy it again on GMG (or until they have a gift option, which could be about the same time frame - never)
Even when they are Steam keys? (like this one..)
Yes, you cannot have more than 1 copy/ license of game in your account, the DRM doesn`t matter.
When you log-in and what to buy the same game again, the Buy-button is removed.