Ok I've put a BUNCH of rounds through a MKII and I am the owner of a new MKIII.
1. They are not that hard to take apart. When they are new, the guns are still and you may need a punch and mallet to get the frame pin out, but they loosen up over time. They are not that hard to assemble either, you just need to remember to point the muzzle up when you put the mainspring back in.
2. IMHO, the MK2 and MK3 are about the same in terms of pro's and con's. I used a MKII hammer bushing to remove the magazine disconnect safety on the MKIII. The MKIII has a magazine release button which is in a better position than the MKII which has a latch at the bottom of the grip. On the MK2 I installed an extended mag release to make that easier. The MKIII has a loaded chamber indicator (LCI) and while some people do not like it (you can get a filler piece to remove it), I actually REALLY like the LCI because it quickly tells me in competition if I am DEFINITELY loaded or not without having to slide the bolt back slightly. Sometimes the MK pistols will not pick up the first round when you slingshot the bolt with certain mags/ammos.
3. I also put in a VQ trigger kit and VQ extractor in the MKIII. I am not very mechanical, but I was able to do all of this work on my own.
4. These pistols are very reliable and very accurate. You can't go wrong with one.
Don't be afraid of the MK's; they are not that hard to take apart and put back together. The first time will take you a little bit; it took me about two hours trying to figure out the 'tilt the muzzle up' part. But I can strip a loose MKII or MKIII and put it back together again in under a minute. Its really easy once they loosen up.
Finally, RimFireCentral is THE place for these types of questions. The guys over there have forgotten more about the MK pistols than you'll ever know.