Fashion statement or defensive gun?
I would guess that this is the type of gun you are describing as a derringer. This is the model 1 of the American Derringer Company in Texas:
Caliber: .45 Colt
Length: 4.82 inches
Barrel: 3 inches
Height: 3.35 inches
Frame width: .9 inch
Grip width: 1.2 inches
Weight: 15 oz.
2-shots with automatic barrel selection
I'll admit that it is an interesting gun with some historical interest, and that it fires a significant caliber. The problem from a practical standpoint is that it has to be thumb cocked before each shot, which probably takes two hands and is slow. And it certainly has a heavy trigger and minimal sights, so that it would be very difficult to shoot with much accuracy. Finally the two shot capacity is pretty limited.
I'd hate to rely on one of these for defensive use, unless it was to intimidate an attacker into changing his mind. For actually shooting from a 15 ounce gun, I'd rather have a S&W airweight .38 snubby.