Davis Technologies has some interesting units that work a little different then some of the others. I have considered using them in the future, not for racing so much but with lots of torque on hand as a safety measure on the street. (Not street racing) I looked into it a while ago and I don't think they are any cheaper but they may be easier to install and have less to go wrong with them? I don't really have any first hand info but I'll throw it in here since you were asking. Here's a link to one of there videos.
http://www.moretraction.com/imagesmo..._16_10_v1.html