IMHO it seems like a bit of a con to me. If it could produce all the effects it says it can, ALL the motor manufacturers would fit them as standard, and Subaru wouldn't of had to introduce the 2.5 to beat emmissions.
I've not looked into it to hard, but it seems to be fitted to a VACUUM hose. Vacuum hoses don't, as far as I know, introduce swirl. They control things like cold start, and provide feeds to the ECU. This seems to act like a leak in the hose, causing less vacuum, and possibly (depending what it's connected to) leaning out the fuel. NOT good on a Scooby.
Don't take the above as gospel, I'm just thinking it through.
Ready to be shot down[:^)]