I originally purchased the Bactrack S75 Pro and used it for a year, until it was stolen. It was great, but in replacing it I decided to try the BACtrack Mobile Breathalyzer. I like this even better! It's about 1/4 the size and fits much more comfortably in your pocket. The iPhone app is easy to use, bluetooth connects quickly, it and provides a better interface than a small screen on the breathalyzer itself. I also love the ability to graph your BAC over time (although these graphs could be improved by making them easier to zoom in and out of, set ranges, etc.). The ONLY downside to this device it that you now need to make sure that your phone's battery (and your friends') does not die.
The scout can give some false positives if you don't wait the required 20 minutes. Although, I used the scout in multiples of three and mentally did an average just to be sure. Overall, this is still a phenomenal technology in such a small package. I have already recommended it to a friend. Also, the accuracy is to four places after the decimal on the chip, beating the next best unit for the price, i.e. the Element Pro.
Turning this device in yearly, while not being a hardship, is certainly inconvenient. But, for a precision device, I'm sure this is necessary for accuracy.
I bought this product after I got my first fyi since I am older now. I just did not realize I could not drink 2 glasses of wine with dinner and not have a bac below .8
I use the BACtrack as a pre-test before blowing into my state monitored interlock device to start my vehicle (don't want to take a chance there). In terms of accuracy, assuming that the hard wired monitor from Intoxalock is spot on, the BACtrack consistently reads high, which although certainly better than reading low, does put into question BACtrack's consistent +.012 overage compared to the Intoxalock. That is the sole reason for nicking a star off my rating.
Very positive about the size and very user friendly, only problem is that you cant drink so much before you reach the legal limit of 0.05, but guess that's not the machine fault :-)