I bought this product a few month ago and have been happy with it. I don't have any real ways to measure how accurate it is scientifically but when I've been drinking and use it, it seems to be accurate with how I feel.
I bought this one after owning the keychain for 8 months. This one is way more accurate, more than .02 times accurate than the keychain. Worth the money. On the keychain you will blow .02 times higher than the pro.
I'm doing this review after my first use. It works fine, great precision. The hand strap is hard to fit in place, and the manual has no information about the hand strap.
It's seems like the reading comes out lower then I feel it should every time... Sometimes very shortly (about the 20 minutes it recommends not drinking or eating before using) after I drink (albeit, not very much) it will already read 0.