one thing I'm missing in jjui which jj cmdline does natively is rebase onto multiple heads - using this for quickly testing my branch on some other pr and latest main. other than that agreed, helps a lot with tedious noting down of change id prefixes.
you can do this by using the "set parents" operation (shift+m) which allows you to add/remove parents to a revision. https://idursun.github.io/jjui/revisions/set-parents/
This is something I've never done before. Are you just repeating -o, creating a merge commit?
If that's the case, it also seems like you can do jj duplicate and repeat -o if you just want to create a branch to temporarily test against another branch and main.
yes, exactly this, multiple -o. I sometimes have two or three branches which I keep a single merge branch on top of and being able to switch out the parents is super convenient.