Like drew stated, they are all show and no go. I had one on my spg and it drove me nuts. This was about 4 years ago though. I used it only to adjust the fuel mixture via AMM when idleing. Besides that it's pretty much flash.
You can buy ones for around 125 or so that you have to place into the DP via another sensor. These will tell you how your a\f mixture is doing without logging. #r you can get a lm1 for around 400.