I use the medium sized one pretty much every back workout. Didn't buy it, just the last couple gyms I've been going to have them. It's the only bar I use for pull downs. Just find it easy to keep good form, don't need straps when going heavy and it's easy to isolate the lats. Back is probably my best body part, improved a lot in the last year. Can't say it's all due to the MAG bar, I probably just find it easier to establish mind muscle connection (contracting properly) with my lats/back.
Would I actually purchase one, and bring it to the gym? Not sure, don't even know how much they are, and I already carry enough stuff. But if the gym has it, it's my go to bar.