I've got one exactly like the smaller one, and it is the most used tool in my box.
I'm a hot rodder, and play with cars a good bit--Every singe time you've ever needed to apply more pressure than your fingers are capable of delivering is when that hammer comes out.
It also works perfect for delivering light blows when you need to move something heavy, without binding, cracking or otherwise damaging it. I handed it to a friend when we were trying to separate a bellhousing from the back of a block, and he got pissed and told me to get another hammer. While I was walking across the shop, I heard him start to use it, and then he said "Damn... this one's working perfect... never mind!" and everything came free.
Then he marveled at the little hammer for a while.
I found one for sale here a couple years ago and bought it for him.
-Brad