I haven’t tried the UAE4All but I have played around with the BerryBoot idea. I ended up ditching BerryBoot because you can only have one config and cmd file. And say you want overclock, run a different resolution, etc on the different OS’s you can’t. What you change on one changes on all.
I ended up using the “Raspberry Pi Noobs” build because it lets you configure different config and cmd files per OS. Switching OS’s isn’t too difficult.