As a 25,000 miles a year driver, sat nav is essential. Previously had a built in sat nav in the car, but my new car didnt have the option so I had to buy a stand alone unit. Went for this model as I also drive in the US (switching between US and Europe maps is really easy and you also specify a 'Home' for the US map separately).
No doubt there may be problems with defective units, but I feel that a lot of the negative comments relate to the complicated nature of the device. There are a lot of features and I feel that you do have to be very comfortable with using such devices if you are going to get the most benefit from the unit.
For me the live updates are invaluable and have used the cheapest fuel feature to save money, and google to add favourites that were not easy to find the adddress of. Also the IQ predictor of arrival times is uncanny ... recently predicting a hour journey almost to the minute.
I have also had no problems with connecting my phone and using the FM transmitter.
In summary very happy with this device.