,

Probably quicker for them.

As much as I like Steam, to me the GOG version is the best one for a game such as this. It's such an old game that it won't take advantage of any of Steam's features such as achievements, cloud saves, trading cards, etc. Whereas GOG at least gives you some neat extras and compatibility updates for newer Operating Systems. Free is free of course and you take what you can get though, even if it's uPlay.

Just log in to your Ubisoft account and check your game library

I'm guessing it's probably a targeted promotion that is automatic.

It should be in your Uplay library automatically.