If you are already a heavy Magit user, then most of the basic ideas will probably be appealing and jj will let you bring those ideas to the command line. It will let you do some acrobatics you thought weren't possible before, ones that many users have come to love -- like rebasing a 5-way octopus merge with 2 extra leaves that result in conflicts you don't have to solve yet. (This is a technique known and popularized as "Mega Merge", which I suppose I am responsible for "inventing" along with its semi-silly name.)
I think Magit is an interesting parallel to jj. You say the "magic of git", but for both of them I think most of the "magic" has less to do with Git and more to do with the "design language" exposed to users, and by that I mean the tools that allow you to manipulate, navigate, and arrange commits (and diffs!) Git is more like a physical storage layer for both Magit and jj, but beyond that a lot of the special sauce is unique to their algorithms, their UX, and their "nouns and verbs".
In my experience, Magit users are generally harder to sell because for them jj isn't so revolutionary; die-hard Git powerusers who have been exclusively slugging it out on the command line to perform 10-stack rebases for the last 5+ years tend to be very easy to sell, in comparison. But all these users tend to understand and appreciate the power of a well-designed set of tools for commit graph manipulation. Git powerusers tend to be some of our most hardcore converts and advocates, really.
Full disclosure but I'm one of the jj maintainers and my opinion is that it's pretty good. Maybe try it out for a few days (perhaps without using Magit, if you can :)