The understeer.com SSK is the same shifter as the z3 M which is the same as the uuc, but far less. Get it.
I went the very cheap route and bought a used M5 shifter, which has a shorter throw then my 540i. The M5 shifter isn't as short as the understeer, but short enough.
The problem with SSK is that if the throw is too short, it is easy to mis-shift say from 5th to 3rd. People will deny that they do this, but on the track when you heading into a turn in 5th and need to be in 3rd when you come out of the turn, it happens and you can over-rev your engine. With that said, I love the shorter throw myself.