The pepperbox revolver was a very popular firearm used for self defence back in the days. But how powerful was it?
Well a .36 caliber revolver of the Colt type, loses some of the gas when the ball jumps from the cylinder to the barrel, due to the gap... then after the ball exits the cylinder and enters the forcing cone to be swaged onto the rifling, which causes friction and would slow down that ball just a tad.
While the Allen pistol each shot has it's own barrel for each shot to move to the muzzle. So it's likely that with identical loads..., the Allen type pistol would deliver higher muzzle velocity (all other things being equal). Would this advantage be significant? One might want to chrono the two to see.
THEN you have the double action aspect. One might tear though a full cylinder, launching the contents into an opponent very fast, compared to the same when using one hand on a Colt Style revolver, and thus at close quarters, putting six shots into an opponent in four seconds or three shots each into two assailants up lose in the same amount of time, might be quite powerful indeed.
On the other hand, Mr. Hickok demonstrated on at least one occasion, if my memory serves, that the gap from the cylinder to the barrel not very significant while he launched a lethal,
aimed shot across a large intersection in a town, dispatching his opponent with the shot. So aiming and longer range might make some consider the Allen & Thurber pistol not that powerful compared to a Colt style.
I'd suggest that one carry both. The double-action Allen and Thurber for
up close and personal fast shooting situations (like at 7 feet or less), and a Colt .36 Navy for encounters at a distance OR if one emptied the A&T inside the saloon, and exited, followed into the street by the adversary's friends.
AND one could start with the Colt style if out in the countryside and engaged at a longer range.
LD