It's a good product. It is simply a multiplier for your tachometer signal. It is no more or less accurate than other methods to correct your speedo (i.e. chip). It is simple to install. I did it in about 30 minutes...and that was going slow with multiple beer breaks.
I completely agree. It was easy to install and works great. Also, you can adjust it for tons of different gear ratios from like 2.73 to 6.3x. This means that you'd be able to compensate for, say, 28" slicks. Just my 2 cents.
Not only is it a good product and easy to install, but you absolutely can't beat the support that Willie - Triblkcobra (sp?) will give you if you have any problems. I couldn't seem to get mine dialed in for my 4:10's and he worked with me to get the settings right to compensate.