It seems to me like it was designed for two finger shooting. The index finger would be on the front trigger and the middle finger on the rear. If so then the trigger hand would not have to be moved on the grip between shots.
They would have had to rework the seer on the rear trigger as the extra leverage would reduce the pull force by one half and magnify the actual movement of the finger by two.
From the description in the ad I take it that the trigger is an aftermarket addition although I am not certain of that.
