I have had the MPGuino installed and dialed in for about 5 months now and can personally say that it is worth it !!
I see no other way to gauge your driving habits/conditions on the fly without having this little rascal installed !
I had an unusual glitch with mine when I originally installed it that was a chip failure, but contacted the seller, sent it in, paid for the repair and got it back. It did take a bit of time for that whole scenario to play out, but worth it.
So, PROPS to the MPGuino Brainiac who built it !!