Highly recommend anyone try this out, I love it. Threads matched up perfectly on the shift lever and the Skunk2 knob i have.
Still.. when you increase the length of the shaft, you are also increasing the length of the arc at the top of the shaft... increasing the length of the throw! Not by much.. but some...I can't see this being very effective on a stock shifter. I run a ch knob and extender on my 99 civic. But I'm also running a skunk2 short throw.
The purpose of this extension is to make your reach from your steering wheel to the knob quicker. That way your hands can get back on the wheel quicker. Usually for circuit racing.
The poster above saying about a shorter shifter.. People are usually looking for a shorter throw not a shorter shifter. That takes place from the pivot point and where it bolts to the linkage. The longer that is the shorter the throw.