I have a couple of 642's and had a couple of 637's. Nothing wrong with the 637's, just didnt see the point in keeping them, since I shoot everything DAO anyway. The 642's are more pocket friendly too.
If youre going to carry them with minimal grips, which realistically make them a lot more concealable, or even with the larger grips (never understood the thinking here), Id highly suggest you try one out with ammo you would likely carry in them before you commit to one. They really are not very pleasant to shoot, which tends to discourage practice, and limit proficiency.
I still shoot mine a couple of times a month, but normally quit at a box of fifty, as my hand starts to rebel, and is usually sore for a few days after. You do need to practice regularly with them to stay on top of them.