Which one are you thinking about? I have the electronic shift-plus and love it. It just firms up the shifts and makes them quicker. Gears are held for a bit longer, too. The install was easy, took about 30 mins.
The "box" has 3 settings: I call them 0,1,2. 0 = stock, 1 = medium, and 2 = hard. I usually keep it on 1 all the time, 2 when I'm racing. 1 is more firm than stock, but just right. 2 is a little too firm for me, but good for racing.
Only 1 problem: the resistor box gets really hot. I took some cheap computer heatsinks, some heatsink gunk, and some electrical tape and put a heatsink on each side of it. Cost me $2 and it keeps the unit cool.