I have tried Galaxy 1.x once, but it failed to install due to some bug (which seemed to be pretty common back then). Never tried 2.0.
After that I haven't dared to install any Galaxy client after I learned that installed GOG games, even those installed with offline installers, would automatically launch Galaxy whenever I just try to run the game. I've heard conflicting stories whether or not that is still the case.
Some say "but you can run the .exe directly or edit the shortcuts for all your installed GOG games", but frankly that just sounds too much of a trouble, especially for DOSBox games whose shortcuts are quite complicated. With DOSBox games, I don't think you "just run the exe". You have to run DOSbox executable and direct it to correct config files and shit.
So I am not against installing and trying out Galaxy (1.x or 2.x), but I am against the idea that installing it in any way affects or touches my offline installed GOG games. No thanks, that sounds too much like that Microsoft Game Explorer shit that starts messing around with installed Windows games and then causes this:
https://www.gog.com/forum/general/old_games_not_launching_and_eating_100_of_the_cpu_on_windows_7/page1 HANDS OFF OF MY GAMES! I'll tell you when I want to use you, okay? The genie shouldn't come out of the lamp before I rub it, not on its own "Oh, master, sorry to wake you up, just though to check whether you want me to do something? I hope you don't mind that in the meantime I rearranged everything in your room?".