You don't get PC software as good as TomTom Home with the Navigon, and there's no Mapshare facility that allows you to share in other users' map corrections for nothing. However you do get free map updates for a year with a refresh once every three months, which means even where major roadworks alter road layouts dramatically, your sat-nav should be able to keep up.
But it's not all good news. Despite the fact that the Navigon 2100 has a SiRFstarIII chip on board, which ought to provide quick satellite locking and reliable position display, the Navigon 2100 manages to somehow stuff things up. This device seems quicker to lock onto a position than its the 2110 Max was - I never had to wait too long for it to get up and running - but it did struggle to maintain a solid signal in built-up areas.
On one of my test routes, which traverses London from north east to south west, it became seriously confused around Blackfriars Bridge: it asked me to perform a U-turn when none was possible, the icon representing my current position started to point in random directions, and it repeatedly recalculated the route for no apparent reason until I emerged into more open space.
For all that, the Navigon 2100 is still a very competent sat-nav. It's not perfect by any means, with fiddly address entry and the occasional satellite signal drop-out, but for £100 it's a very competent, usable navigation system.
With speed camera information (plus the potential for TMC traffic info), and an excellent mapping engine, some very nice route planning tools and a comprehensive POI database, if you've £100 to spend on a sat-nav system, you won't go far wrong with this.
And though it may occasionally be a little unreliable in very built up areas, for 99 per cent of the time you'll probably not be driving through forests of skyscrapers.