The J frame revolver is a very close combat defensive handgun. If you need to defend your life with it, the situation will be close, and very quick. I doubt you will ever have the time to thumb cock the hammer before you need to fire.

I carried a model 60 as a undercover and back-up gun for years. Mine was am issue gun, which meant it was not suppose to be modified in any way. One day I was at my local gunsmith, and I guess I was standing too close to the grinder, and the hammer was accidentally removed. And by some miracle, a heavier hammer spring was installed. Even after the "accident" the little Model 60 performed well for the next 12 years until I retired.

Now I have a 642 and a Model 60, along with a Colt Detective Special and Colt Agent. All the exposed hammers have been bobbed.

IMHO go with no hammer for a pocket gun.