MIM is as good or as bad as the process and the material. Good MIM is very good. Bad MIM is worse than bad. The stuff that Kimber used in the beginning was very good. Now...not so good, apparently.
None of the manufacturers make their own small parts, and many don't even make the slides and frames any more. They've gone from being gun makers to gun assemblers, and their quality...or lack thereof...is at the mercy of whomever is producing their parts.
Colt has a good MIM vendor. I once laid a Colt MIM sear concave side down on an anvil and hit it several times with an 8-ounce hammer. It didn't break. Not only did it not break, but it functioned normally when returned to the gun. Then, I removed it, turned it on its side, and hit it some more. One of the legs bent, but didn't break. I clamped the disconnect in a bench vice and smacked it a few times. It bent to about 15 degrees and finally broke. The chances of breaking one of those parts during normal operation of the gun would be so infintessimal, that you could go ahead and call it impossible.
Note that I don't consider that to be representative for all MIM parts from all vendors. Only that those MIM parts didn't fail on that day when subjected to stresses a few thousand percent greater than they'd ever be normally subjected to.
As a rule of thumb, if an MIM part is going to fail, it'll fail early on. If it lasts for a thousand cycles, it'll likely last for 50,000.
Eddie...There are no cast or MIM parts in a Norinco. Everything is machined steel. The issue is that it's fairly crude, but they can usually be greatly improved with a little judicious polishing where applicable. Not all of them need any. Others need it badly. Springs should be replaced right off the bat. Their OEM magazines are excellent.