Well, I can't get on board with either of the two posts above mine.
The magazine release is absolutely an improvement and unless your vocation is a European police officer in the 1970s, a heel mag release is an antiquated and entirely un-modern design. Changing that was perhaps the biggest draw to the 22/45 series pistols when they were first released under the Mark II banner.
I can certainly deal with my heel mag release, and it's not a deal breaker. After all, I am used to it. It's perfect in functioning, it's just slow and methodical to use. If you elected to use your heel-release equipped Mark II in some manner of a speed competition, it would be an impediment no matter how skilled you may be at it's use. To argue otherwise is to be dishonest to the discussion.
If anything, you can make the argument that it really sucked that all the non 22/45 Mark II owners could no longer use their collection of magazines for the new Mark III pistols, but otherwise? The magazine release on the Mark III is an improvement.
The other thing that simply hasn't been mentioned enough is also quite difficult to argue against, if we'd all just be honest: removing the LCI is certainly easy enough, but please
let's not skip over or gloss over the fact that it leaves a gaping, nonsensical and horrendous looking oblong HOLE
in the side of the pistol.
You could formulate an argument about grit, dirt, lube, or what have you... but a simple and common denominator is that it's a damn eyesore. Certainly, aesthetics are quite subject to opinion -- but the bottom line is that the pistol looked
a particular way for FIFTY-FIVE years... and then they machined a rectangular HOLE in the port side of it.