I have used them myself on occasion, more for a reference and for skimming through, rather than actual fully focused learning. I think they are good if you are complete beginner, although if you already have some experience, you probably will not learn much. Most of the value there is that they encourage practical examples and writing GDScript in the browser, but you can gain experience with that in your own projects too.
Overall, I think it really depends on your particular situation and what your goals are.
So I complete the 2D game in the browser and not in Godot?
If you want to learn more about GDQuest, you can see a list of projects here that people have made following their courses: Search results for 'gdquest' - itch.io I would say that the fact they are on itch.io is a good sign they teach you how to do that. But playing the games that people have made in their lessons might help you decide.
You can also try their free course here: Learn Godot's GDScript From Zero by GDQuest It runs in the browser, or you can download and run it on your computer.
If you’re willing to drop money, but not that much, this Zenva Humble Bundle is 25 courses for $25. It’s a great way to start, and you are less likely to have buyers remorse if you’re taking a chance sight unseen. I got their last Humble Bundle and even as amore experienced Godot developer, I felt I got my money’s worth. Here are a few posts I made on their stuff before: