I have it on my BRZ. I do track my car too. Usually six times a year.
I did get my Tein Street Flex brand new for dirt cheap through the closeout sale. Have been to Buttonwillow with it installed once. It's a no brainer choice for people who are looking to have fun at the track, especially with the price point it's being dealt at. Love how firm it is at the track with it. The ride is very nice at the softest setting. Some of my friends can't believe how smooth the car rides.
Here's my set up:
17x9 +35 RPF1
245/40/17 RS3
Tein Street Flex with -2 camber all four corners
DSC_0113 by
JS + MS3, on Flickr