First thing first. The speycast is a flyfishing cast whether you use a single handed fly rod or a two handed fly rod: the cast remains the same. All fly casts are initiated and executed with the butt of the rod.
If we look at a two handed fly rod we see that there are two parts to the handle. The reel is the axis which we build the cast around. The top part of the rod we consider is "north" of the reel, and the bottom portion of the rod is the butt or lower grip.
The straight line path of the rod tip (is what all good casts are built around) is governed by the rod butt. The longer the straight line path of the tip, the more efficient the cast. Remember, it is the rod butt that determines the straight line path of the tip.
What Zpey has done with their proprietary lower handle on the rod butt is provide the caster with 10 to 15 degrees of longer of tip path with the offset handle.
What Zpey has done with their proprietary lower handle on the rod butt is provide the caster with 10 to 15 degrees of longer of tip path with the offset handle.