Hertz uses Magellan in their cars, and I always rent it, have for years. The system was a little cumbersome and sometimes lost its position in dense city streets, but today it is always dead on, especially in large cities like you are driving in. And the Yellow Pages and Intersection functions are extremely useful, the street address is a little more cumbersome but useable. I find it useful even in areas I am familiar with, for example finding the freeway exit in pouring rain or recomputing a route around construction, all done automatically.

My suggestion is go rent a Hertz car with the "Neverlost" system and see how you like it. I believe this system does have CD's which are loaded for different regions of the USA, the actual system is in the trunk and there is just a small add-on unit in the car, but it is just a display and is not portable. I have never tried one of the portable units, but the only problem I would expect from one would be less ability to receive the satellite signals. If it works where you are, then you should be satisifed with it.