Well I installed th JBD at 1225 miles and now am at 2500 miles....not alot of time on it, but here are my observations:

Definately more mid-range power...especially from 3-4k rpm, butt dyno says maybe 40-50 hp more, i'm running th JBD at the default halfway setting...who knows how accurate my butt dyno is, but its significantly faster as my passengers can attest

I dunno how accurate the onboard computer is but in the drive from home to work my car was getting 27mpg, and now the onboard computer is telling me an average of 31mpg...this could also be the car breaking in more and losening up

I've never had any kind of CEL or other warning, but then again my JBD is set at the mid-way setting, higher setting may cause CELs

Looks its $325, what did you expect for that price? of course you are not getting the most sophisticated tune, then again a $5 bleeder T on a supra MKIV adds 50+ hp....really crude