Weaknesses: Very poor gps fix even when you have an external arial fitted.
Summary: As a taxi driver, the garmin c320 was used 12hrs per night in all conditions. I have had an external arial fitted because it has great difficulty in maintainting a solid fix. Even with the arial, it is not a reliable enough unit to be practical for commercial use. It often drops the gps signal and you are back to using the refedex which kind of makes having the unit redundant.
When it works it works extremely well but for a taxi driver, it can't be relied upon to get you to where you have to pick up the passenger. You might just as well stick with the refedex.
Small enough to lock in your glove compartment when parked and not in use.
Weaknesses: Surpassed my expectations and works wonderfully.
Summary: Originally, I wanted an integrated system for a cleaner OEM look. These cost $1000+. I chose a portable one to save some money and discovered later that portable is the way to go b/c it can be moved from car to car very easily. You can share this unit with friends and family!
Even in remote areas like Boreal snowboard resort, streets were named accurately and directions were perfect. The unit initially did not recognize the address going there, but led me back home from the resort very easily.
This unit recalculates new routes within 5 seconds. If you stray from the original route, it will calculate a whole new route to get you where you need to go. I can imagine some units bring you back to the original route without recalculating a new more convenient one. This can lead you in a circle. You won't have to loop back with this unit.
Wireless is great! I hate plugging stuff into the cigarette lighter and having wires dangle everywhere. This unit is rechargable via cigarette lighter or a/c plug.
Screen quality is better than shown in most photos on the Internet. I was very surprised when I first picked up the unit. The quality is all there.
Unit provides addresses of businesses, gas stations, parking lots, retail stores and others with phone numbers!
New maps can be updated into your unit by downloading them from the Garmin website.
c320 is a touch screen unit which definitely helps speed up the data imput. It also has a larger screen than the entry level Street Pilot i2 and i3 models. The bottom of this unit is flat so it allows you to tape it to your dash or creatively place it wherever it works best for your car. This is where I placed mine: http://www.cardomain.com/ride/351327/27 I imagine it may lower the satelite reception, but it's worked fine for me so far. I only lost reception on bridges and in tunnels which is expected.
Unit saves your previous routes so you can conveniently access it again without punching in the address all over again.
I'm the type who gets lost all the time and have a horrible sense of direction. This unit has made me feel much safer in areas I'm not as familiar with. Even in areas that I drive regularly, I'm learning street names that I had never had the discipline to notice before.
As a whole, Garmin produces units for every budget from around $200 and up. You can get some used units for even cheaper.
Reviews on this unit have been great and that's a big reason why I took the plunge and bought this unit for myself. Search online for more reviews of this product to see the differences between other units your considering.