I haven't done any AR mags, but did do some Walther P-38 magazines (and the internals) with Brownells Teflon/Moly coat.
Ideally, if you can sandblast them a bit, that would be good. But the big trick is to make sure that they are COMPLETELY de-greased. Use something like "Gun Scrubber", or for a cheaper alternative go down to the auto shop and get some carb cleaner spray.
I used a heat gun to pre-heat the parts and dry the coat as I sprayed it on. 2-3 coats, bake in the oven per the directions and BAM! You have a slick durable finish.
I have some UZI mags on order for my 9MM conversion and I'm thinking about doing the same to those mags (if needed).
Joe
Sorry, forgot to answer your questions.
It worked good but is it worth doing? If your magazines already work fine and don't need re-finishing, I don't necessarily think it will make them work any better.