I have a Navman iCN520 and it really poor for a GPS but I got what I paid for. It takes too long to register satellites. Took about 10mins standing in the same spot to put a dot on the map and it's a common occurance where I might be driving a good 15km before it all registers. No clouds, no tall buildings with glass to fool the GPS signals etc... With the iCN510, wear polarised sunglasses and you can't see the screen. I ran one for a while as a loaner from work. A problem fixed in the 520. The screens are also too small to see from the dash and best mounted on the side window but the suction mounts will ruin tint if you have tinted windows. Well, any suction devices on tint will wreck it so don't do it. Conclusion for the 520, I passed it onto the better half that doesn't use the car all that often. Nothing beats integrated because it also gathers in steering inputs, speed sensors so if your going in a long tunnel, they'll know pretty accurately where you are under the ground. None of the portable ones have this feature (obviously) and something not many people know about. Pretty important if you are underground and there's a turn off. Disadvantage is of course price.