I've yet to hear anything negative about any of the short-throw shifters available for the Impreza.
The STi version is wonderful, of course...it's made by STi. The STi version is also expensive, of course...it's made by STi.
Shiv, the "mastermind behind SCC's Project Impreza RS," has used the SYMS version and hasn't complained. He also hasn't mentioned it since the installation.
I've read numerous posts regarding the functionality and price of the Kartboy shifter. Nobody has complained, everyone has raved about how inherently good it is, and I see a lot of people recommending it.
Those three are (I think) the only ones about which I've heard. I've heard that there are differences between the shifters because the length and curvature of the post offers different "feels" for drivers. Namely, I've heard the STi shifter is excellent for auto-x and rally racing, whereas the Kartboy shifter is more in line for daily, quick-shifting driving.
I have yet to install a new shifter, but I don't think you can go wrong with any of the three. I also donít believe any of the shifters are difficult to install. I hope this helps.