I went to the LGS and bought 200 rounds of 5.56 and saw a Caldwell Tac 30 mag loader and had to have one. It makes short work out of loading 30 round mags and saves wear and tear on these old thumbs.
I've had a loader for a few years now, but I haven't even taken it out of the package. Since I don't shoot my AR very much, I can hand load the mags just fine without one.
I've never used one, but they might prove useful if you were loading many magazines at one time. Comparatively, .223 AR magazines are about the easiest of magazines to load.
That's what I was looking for but they had a Caldwell set up on the counter and when they showed me how fast it was I changed my mind. With a little practice you can dump a box and a half of ammo right into it and hit the plunger three times and it's loaded.
I have the Maglula. Saves time. In NJ we can only have 10 round magazines, so I normally take 10 mags and the Maglula with me. I would rather use the speed loader than take my time hand loading.