Some of my 9mm pistols are able to be dry fired without a snap cap, but my Kel-Tec PF9 requires them.
It is a very cheap way to learn trigger control and break in your trigger by using these caps.
I've dry fired my Kel-Tec about 150 times so far, and I'm still on the first cap. I'm not sure how long one cap will last, but I think I'm going to wear out before it does.
Pros: as advertised
Cons: none
This review was written in the old system and had content requirements that are different than reviews written today.