How well does the handheld GPS systems work or preinstalled is better?

Portable GPS receivers are generally lower cost and at least as good as pre-installed models. Sure, it may not be built into your dashboard, but you can carry a portable GPS receiver into your spouse's car or into a rental car. It is also easier to update the maps on portable GPS receivers - you either connect them to your PC to download the update or insert a memory card to do the update.