If you want absolute accuracy and affordabilty get the
mpguino. If you want features and to be able to watch other sensors (which is quite important) get a
scangauge. The kiwi is a 'neat' gadget, but its slightly inferior to both of the other two if you really want a good tool. I wrote up a review of it on our blog. Do a search for kiwi there and I'm sure you'll find it.