My second Derringer is one of the Freedom Arms 22 Mini revolvers. These guns have a four shot cylinder, I have a 22LR and a 22 Mag cylinder.
I carry this gun 100% of the time, here at the house with CCI 22 Shotshells, for snakes, and when I leave the house I load it up with 22 Mag HP ammo.
When deer and pig hunting I usually carrry it with two CCI Mag Shotshells, and two 22 Mag Solids.
I have killed several snakes with it, including copperheads, diamond back water snakes, up to 44" and a 54" rattlesnake.
I have killed a couple of squirrels, a couple of rabbits, both for the pot, and used it for finishers, ie head shots on a few pigs.
Again with practice it is scary accurate.
The advantage with a Derringer is that you can carry them on your person, or "about" your person in places that you cannot carry any other type of handgun.
Personally, I would never carry one as a number one, or not even a number two, but they make a great number 3, and number 4....
If you do get one, or more of them, practice with them. You just might be suprised at how well they shoot...