I have both the SR22 and the MkIII. Like the SR22 but LOVE the MKIII.
The SR22 a super fun shooter and a great little gun to teach a new shooter the ins and outs of a semi-auto. Easy to use with highly visible manual safety and double and single action. Also, simple to take down.
The chrome, bull barrel-ed MKIII I have, is just awesome. Looks great, has nice heft to it and is a stupid accurate tac driver at 50ft. Lots of ways to pimp it out if you so choose. The one drawback is that to the first time owner/shooter, its kinda bitch to take down and harder to re-assemble. Especially a new one. Even with videos and practice, it'll take you some time to master getting the hanging thing-ie in the right position to get that bolt stop back in. But once you get it and the parts loosen up, easy peasey!!!
One interesting note... side by side... with the same ammo, I noticed the MKIII knocks down the steel plates at my club. One shot, one plate where it might take 2 - 4 rapid shots to do the same with the SR22.
Also if you shoot .22, you shoot A LOT of .22, so this invention for the MKIII is a MUST HAVE!!!! McFadden Ultimate speed loader!!!! It saves your thumb, but it'll costs you in the wallet, because with one of these you spend all your time slinging lead and very little reloading. They NEED to make one for the SR22 and if they do.. point me to it.
https://www.youtube.com/watch?v=6wFM9YFbKak&nohtml5=False