Ive had a couple of 642's with the lock for a number of years now, and never had any issues with them. They get shot a couple of times a month, and have quite a few rounds through them now. One is a little sloppier than the other now though.
Im kind of "meh" on the locks. Theyre there, who cares, I dont use them, they havent been a problem. The guns work just like the guns that dont have them.
My 642's have been used/shot on a pretty regular basis, and show it. The finish while not ratty, does have character marks. My buddies 442 of the same vintage on the other hand, looks like it was drug behind the truck, and even the slightest wear is much more noticeable and obvious on the black gun.
I had a 940 that used moon clips, and Im kind of "meh" on them too. While they worked, I found the moon clips to be somewhat finicky, and as was mentioned, they had a habit of loosing rounds when kept in your pocket. They also sometimes got tweaked, and loading and extraction, was sometimes difficult. In the 940's case, they were basically needed, with the .38's, I prefer the Safariland Comp 1 type speedloaders. They are more secure, dont lose the rounds unexpectedly, and are fast and easy to use. Not as fast as a good moon clip, but pretty close.
For grips, I use the old school S&W service type grips with a Tyler T grip. You wont get any smaller, and I find this set up is also the most comfortable to shoot with. Not that these guns are comfortable to shoot with mind you.
