Well first I bought my SB off eBay for $250 delivered to my house. Arrived in 3 days, super fast. Installed it and WOW unbelievable. I feel like I just traded for SRT6 set up. At least off the line. Its raining here and with wet roads if I give it the gas from a stand still my 20" rears spin and traction control comes on. I would have no problem in recommending the purchase from this guy: http://www.slkfans.com/. I have now over 1,100 transactions and can tell you this guy is above board and a stand up guy. This is a better mod than my last car I used a tuner on. Best $250 you can spend.
I also did not remove the nut on installation. I tried but could not get it. I removed the console side panel (two phillips screws) and then just unplugged it at the top of the pedal and plugged the SB in. Put the side panel back on and in 10 minutes I was having a ball on the road.