I had an N810 and I used a couple of gps/map programs on it, but neither were complete enough (at the time) to get much use out of. The one that I remember I think was called NavIt. It showed a lot of promise, but it couldn't do offline navigation. 

The TomTom is like an iDevice in that it "just works." Meaning of course that it just does what it does, and nothing con be done differently than the way that the manufacturer has decreed. There are a few settings accessible to the user, but not much of any consequence. I bought mine used, and I'd buy another used one if I needed it. I'd even pay full price if I had to, but I'd never buy one on the primaty market; casting my dollar vote for the way that the company behaves. They make devices which run a Linux kernel and they lock the device to their own management software, which only runs on Windows or Mac (and poorly at that).