Just want to point out that this is a command line tool which is why when you click on the executable it will open a window and close quickly. You would use it in conjunction with the CMD and navigate to the location on the command line OR with a third party application like WolvenKit.
Official support is never a bad thing. Outer worlds promised this centuries ago and it never happened so it's great to see CD Projekt Red follow through and do some so cool.
It's nothing particularly crazy in and of itself. All this does is allow modders greater depth in the sorts of mods they can create. However, thanks to this, the mods the game is getting are essentially addressing every single gripe people had with the base game and then some. All you have to do is look up a video or two showcasing all the ways you can tweak the game to your liking and voila, you have the Cyberpunk 2077 that you (reasonably or unreasonably) expected.
What's more is that, thanks to the way it works with Galaxy, you can quickly go right back to the vanilla game with the flip of a switch, without the need to do separate installations. I hope that companies like Bethesda take note for this, as it'd save everyone a LOT of headache if every game was this simple to mod. I've been playing and modding Bethesda's games since I was a kid and I can't tell you how many times a feature like this would have spared me hours of frustration when I really just wanted to play the game (with or without the mods). It's also great if you just wanted to start fresh and it means that nobody will be left waiting for mod updates when Phantom Liberty drops.
So yeah, if you like the base game in any way, I highly recommend downloading this and taking a look at some of the awesome stuff the community has released so far!