Supporting GOG feels great, they are the most friendly game distributor by far. Steam is a huge mess, every time I install something from them, can't wait to finish it and remove the whole platform asap.
I don't know what kind of Early Access this will be, but based on previous titles (Divinity OS 1 & 2), Larian will finish this game, instead of keeping it EA "forever" as many do on Steam. So I would buy it at full price already, on GOG, if it's released earlier. Looks like it's a game I want to play, though maybe won't have time next months, so won't be a problem waiting for full release. Every Larian game I bought on GOG so far, gave updates for free, so they really deserve an early buy, especially for a game like this.