but Nuuvem makes me nervous with is "Brazilian store" aspect. What if Steam restricts those purchases to Brazilian IP's only ? and i prefer to keep all my games on Steam, as opposed to GOG.
Like I said before, most of the keys you're getting on G2A or Kinguin are either Russian or Brazilian. It's why they're so cheap. There's no sorcery behind it

Just some extra info, all the stores I saw selling Witcher 3 pre-orders (except for Steam itself) were selling GOG copies, which makes sense because obviously CDPR will want to push their own storefront, not one of their competitors. This makes me think that Kinguin/G2A/whatever are selling keys for a game that they don't actually have stock of yet. Otherwise, why wouldn't they send you your key so you can activate it so long? Seems a bit odd.
When you get a key from Nuuvem (or actually most online stores - including GMG and retail copies), it's usually what's called "ROW", which means Rest of World. In other words, you're getting a 'generic' key. Valve can't retroactively region lock keys, it's out of their control. Only steam gifts bought from their own store can be retroactively region locked. Go to
this page, and have a look through it. No doubt you'll see a couple games which are ROW copies.
Nuuvem states, usually in big red lettering, when a product has a region lock. They know a lot of their business comes from outside of Brazil, so they make sure to properly identify any potential issues for their users. As far as I'm aware, I've never seen anyone mention having a game region locked after they've already activated it. As I said earlier, Valve doesn't have the ability to retroactively region lock licenses bought from outside of their store.
This was a pretty popular thread, if you want to do some more reading.
To each their own on that one. I prefer not being locked down to a client to play my games, but that's just my preference

I also like GOG, subjectively I think they're a better company than Steam.