My experience has been very similar to CBS (previous post). I too have the ESS VT-1 535 kit purchased through IND, and I have been thrilled by the results! Mine was installed when the car had 4,000 miles on it, and I now have about 6,500 miles on it.
I had my kit installed by a very solid local speed shop. They found the installaion to be very straight forward. They also found IND/ESS to be very responsive and helpful with the few minor questions they had during the installation process.
For the money, this kit is the hands down best bang for the buck! It gives you near supercar performance with the reliabilty and practicality of a stock M3.
I highly recommend ESS and IND (Nate at IND is very good)