I think it's a bit faster at loading, but not by much. But any gains are very welcome!
What I'd like to see gimp do, if it makes sense to them, is have one menu item that is devoted to plugins. Probably best called 'Plugins'. From there one could find all post-installed plugins in one place. The way it is at the moment really does seem a mess, they're all over the place - in no logical order.
For example, I now have plugins in 'FX Foundary, Python fu, script fu and various other places. It takes a while to find them, and to remember where they are. But if they were all in one place...
I know that's not so much an issue with the appimage itself, but just an idea to make gimp more user friendly.
I'm going to play with this some more, get used to PhF and G'mic, then promote the crap out of it!