TomTom says if you drive an hour per day during peak traffic, you use about 7MB of data a month for traffic updates. If accurate, that's low compared to how much data smartphone navigation apps use, because they're constantly downloading and updating maps and points of interest (PoIs), as well as receiving traffic data. Maps and PoIs are installed on PNDs, so they don't need to download additional data.
TomTom's approach makes sense, and the TomTom Go 500, though bulky, is a quality PND for the price, but you should also check out Garmin's PNDs, including the Nuvi 3597LMTHD. At $330, it's more expensive than TomTom's Go 500. However, it's also slimmer and has a brighter touchscreen that switches between landscape and portrait modes.
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