ESS is fantastic IMO. I have their S/C on my M3 and have had ZERO issues in over 2 years. The 1M tune is via their handheld flasher and I can load the stock file back to the 1M at any time within minutes. The performance gains are significant and definitely noticed! With the ESS tune you can easily take down stock M3's!
See my original post here -->
http://www.1addicts.com/forums/showthread.php?t=557030
