I have both, or I have the 642 and bought the wife the 637.
I pocket carry my 642 but my wife, like most girls couldn't get a bullet in their pocket let alone a revolver, so the exposed hammer is no problem for her.
Any gun, revolver or pistol, in no better then the person shooting it. So practice and rounds down range is the key.
I shoot my 642 a heck of a lot. Besides SD, I use it for plinking instead of 22s. I save my 22 RF Ammo for competition. I can shoot 38s for about $2 a box of 50 ver. $5-6 per box of 50 22s now days. I cast bullets, so the primer is the most expensive part of the round. When I'm too lazy to cast/lube, I trade lead for pre-cast/lubed bullets.
Bang for the buck you wont find more cheaper ammo then 38s so why not use them for plinking? And if its your SD revolver, it makes sense to do move of your pistol/revolver shooting with it.
Shooting is about 90% mental, confidence plays a big part of the mental game. The more practice, the more confidence you gain in your revolver (regardless of the length of the barrel.
Its a tool, used for other purposes then self defense. For example, we went antelope hunting, we got 5, 3 of which had to "finished off", its a simple matter to pull the little revolver from your pocket and put the critter out of its misery. I've used it when I needed to put down one of my horses that had been hamstrung by a pack of wild dogs. I have lost count of the rattlers I've killed in my yard or pasture.
Depend on how you carry, both the 642/637 are excellent little revolvers, and can be very accurate IF YOU PRATACE.
Regardless of what revolver or pistol you have, if you arn't willing to practice with it, you should leave it home. It wont matter whether it has an exposed hammer or not.