Not super so if you wanna mess around with GE-Proton and stuff. Personally I prefer ProtonUp-Qt though. It's a terrible name, but way less flashy, which it super doesn't need to be.
I've used both and found ProtonPlus to be better for my needs. It has way more proton and wine versions available. They also added the feature for steam games to select their proton version from the client as well.
Yea, for sure you can, but you have to go into each games settings one-by-one. In ProtonUp-Qt (seriously, terrible name lol) it's a list with a dropdown box next to each, the steam deck compatibility rating, and the ProtonDB rating that you can click to go straight to the page for it.
Based on the description elsewhere in the comments, they don't sound very similar. ProtonPlus is just a download tool that lets you see and download or delete updates for all the various versions of Proton, so you don't have to visit a bunch of different Githubs. It doesn't let you see or change which version each game is using, which it sounds like ProtonUp does.
I'm not sure how ProtonUp works with native games, installed outside of Steam or Heroic for instance, but it certainly doesn't allow for per-game Proton version changes with Steam games.
EDIT: I was wrong, there's a separate list I wasn't aware of where you can change per-game versions. You can do the same thing in ProtonPlus FWIW.