I have used both the iWay 500c and the Cobra. Perhaps I had a dud, but the Cobra simply sucked performing the most basic road nav tasks. Previous Cobras I have tested worked well, so I don't know what went wrong with this sucker.
The iWay 500c is a lot of GPS for the money, and as I have said before, the best one I know of that combines good on-road and off-road functionalities. (I would expect the 600 to be as good, with a few improvements.) There are others that do street-only better (Garmin Nuvi) and off-road only (Lowrance Baja, several Garmin models, etc.), but this one is by far the best compromise unit out there right now. I think it's good for someone who occasionally and recreationaly goes offroad (or goes boating--it has full blue water charts for all of the u.s. built in as well). It all works quite nicely. Here are the minuses: no internal battery (has to be plugged in to work), slow route re-calculation (as when you miss a turn or whatever and the unit has to recalculate the route; doesn't apply to off-road use), big and heavy (not super portable if you want to take it in and out of vehicles), no real-time traffic service available (if that's important to you).
HTH
Timoss
88 fj62 TLCA