This easy to install device and companion software adds an essential function to my car and promotes good driving habits for maximum fuel efficiency.  I just plugged the device into the port under my dashboard, downloaded the free software, did a very basic sign-up, and it started showing me 'miles per gallon' (MPG) as well as the cost of fuel per trip and for the week.  And it's completely accurate according to the calculations I've been doing until now, dividing the total miles between fill-ups by the total amount of gas I put in the car at the time of filling the tank.  Unlike my method though, I can go back and look at each individual trip, its total mileage, and it's total cost in gas as well as where each trip started and ended.I'm not completely keen on the audible beeps that sound if I brake hard, because when I brake hard it's not out of habit but because someone stopped suddenly or I was avoiding hitting someone who stepped out into the street when they weren't supposed to.  The beep only adds to the minor panic.  I haven't heard it make a sound when I accellerate too hard or drove over 70 mph yet, so I don't know if it's a different sound for those signals.  Thankfully, I can turn the Audible Feedback sounds off in the iPhone app.In case of a crash, you can have the app automatically trigger having up to three people you specify contacted.  That's a great feature especially for those of us who mainly drive alone.Another feature of the app which I haven't had the opportunity to use yet is the engine diagnostics function.  According to what I read online, it is fairly specific about anything that might cause the engine light to go on--from it being time for an oil change to a coolant leak--but again, I haven't had any engine check notices yet so I can't say how well that works or how specific it is on my 2007 Honda Element.  But I do very much like that it will show you a list of all local mechanics right in the app, so no messing with Google or another app--one app does it all.As for CONs, there are none really, but you should be aware that in order to be absolutely sure it records every trip you need to be in the habit of opening the app when you start the engine and making sure it shows that you are &#34;now driving.&#34;  The app doesn't reliably know ever time you start the engine and start recording your trip, even if you keep it open at all times.The same is true for locating your car on the app.  If the app didn't record your last trip, then it will show the vehicle's location the last time it did record it because the transmitter you install in the car is not a GPS device.  The app uses the GPS in your phone instead, and the phone must be within about a meter of the device in order to record and transmit data.The upside of this is, if you don't want it recording every trip then it wont and you can also keep separate stats for different drivers.  For example, you might not want to know your mileage and have your driving scored every time you're commuting to and from work in bumper to bumper traffic, or have your data mixed up with those of the others who drive the same car.BOTTOM LINE: I can't think of anything I wish this app and its sensor did except one.  My car has an alert for when the tire pressure is too low--only when it's rediculously and hazardously low though.  I imagine that means these sensors are capable of telling me how much air pressure is in each tire, and it would be nice if I could see that information on the app.Other than that wish list item, I really love it.  I no longer need to calculate my mileage or remember to reset the trip odometer every time I fill the tank.  In fact, I don't even have to use the trip odometer at all since the app does that as well.I look forward to using this for my Thanksgiving drive between New York City and Western Massachusetts, and my Christmas trip up to Southern Vermont.Love it.  Thanks for adding these functions to my car and phone.