I've got a Mark III 22/45 and it gets way more range time than any of my other pistols. My buddy has a comp model that looks very slick - been thinking about picking one of those up someday.
Only thing that's "tough" is field stripping it - not very straightforward but just take your time and follow the steps right to avoid all of the horror stories you hear out there. I've never had a problem with it. It's chewed up all the bulk Walmart ammo I throw at it, maybe a handful of FTF out of 10k rounds or so, but I chalk that up to more of a 22 ammo problem.
One thing - I stuck a hi-viz front sight on mine (I only run iron sights on pistols). The black on black posts against a black target were hard on my eyes, made a world of difference. I guess that would be the same against any pistol though.
I've put over a thousand rounds through my buddy's mkIV. It's a great gun and I can't recall any ftf or other problems. The only thing that bothered me with that gun is that the mags effing hurt to load after a while. Great plinking gun though. I'll probably end up picking one up too in the next couple months or so.
I usually end up using a spent piece of brass to push it down after the first few.. We've always talked about making a speed loader type thing by taking a piece of scrap wood and routing out the middle just big enough to slide the mag through to push the spring down but we never actually did it. I'll figure something out when I get mine.
Well went down to put teh cash down for the mark four..... ended up coming home with a hi end air rifle instead. Not sure what got me about it, maybe its the 1400 FPS Muzzle velocity, maybe its the fact its deadly silent, maybe its the fact its rated for 100 yard shots, I dont know..... Its A Gammo silent cat elite break barrel design.... Seriously this thing actually shoots very well.