I embraced the idea of magfed for a while, but there are some major problems with it.
First, as mentioned by Gommie, the split in opinion over what constitutes a magfed marker. I subscribe to the idea that it's about creating a level playing field - so the appearance of the gun is irrelevant. If people want to play with candy pink anodised Ego LV1s or Luxes with 10 shot feeds, then that's fine with me, however a lot of people treat magfed as equating to milsim and insist upon 'realistic' guns only, their loss.
Second, First Strike. I can just about accept people shooting FS in an open event against players using hoppers - as the advantage gained in terms of range and accuracy cancels out most (all?) of the disadvantage of having only 10 or 20 shots before needing to reload. In magfed-only games however, anyone unable to afford the cost of FS paint is put at a huge disadvantage. It's bad enough to make me avoid magfed-only events where FS is permitted. Also, I've seen some videos where people say the impact is similar to a standard ball, however practical experience has taught me that's rubbish - they hurt a LOT more!
Third, the equipment. Magfed guns are in general, rubbish. Spring feeding paint against gravity is a stupid idea at the best of times, so the feed systems will always be less practical than a normal gravity fed marker, however even taking that into account, the range of magfed equipment is god-awful. You've got blow-back relics from the early 90s than need springs swapped to change velocity, basic spool valves that make the Ion look state of the art, sometimes-iffy conversion kits for overly weighty and poor performing scenario guns and the general use of poor quality materials and poor tolerances. Even top-end fare like the Dye DAM is dodgy and doesn't even use a Matrix drivetrain, despite the name!
Despite the fact that decent gravity-fed guns can be had from £120 upwards and offer consistently reliable performance for case after case of paint, people are still forking out hundreds for shoddily made, archaic designs that they're lucky to shoot 200 paint through without getting a break or chop.......and don't even get me onto the 'oh I prefer mechs, they're so much more reliable than those fancy electronic guns' crowd - I mean, REALLY? You've got pro teams reliably shooting hundreds of thousands of balls through their Egos, DMs, Luxes in every kind of weather, yet they're still not considered as reliable as some god-awful cast aluminium blowback without a velocity adjuster?
Sorry, went off on one a bit there - to sum up, I like the idea of magfed - or more specifically limited-paint events, but there's too many downsides to it at present.