But how long will they last
Sat Navs are a great way of getting around. However, new roads are always being built or altered. Not all of the manufacturers offer map upgrades for their models. I purchased a Navman a few years ago, and it is still working perfectly well, but the map software is now well out of date, and because the unit is now obsolete, Navman no longer supply any updates. Nowhere when you purchase one of these devices are you told that the maps would only be useful for so long, and you'll soon be faced with a new road layout or even a completely new housing estate and the unit not knowing where you are.
Therefore, it is worth bearing in mind, that you might, like myself, have to throw away an expensive, perfectly working sat nav to buy a new one, because too many changes have occured, and you can't get updates for it.