Garmin Streetpilot i3 - Brilliant
I don't know about the Roadcom 400, but I have had a Garmin i3 GPS unit for about 8 months and found it very reliable and certainly great value for money (I paid about £200 last November).
In my opinion it is far superior to the TomTom 500 which I use in my company car.
It is very compact but in my opinion the small size is a bonus as you can carry it around in your pocket/handbag and even use it to navigate on foot as it can be battery powered.
POI's and "Safety" Camera locations can easily be uploaded from the internet via the supplied USB connection.
I was so impressed with my i3 that I bought a second unit (for my wife to use in her car), a few months ago (£99 from a local supermarket!)
Hope this helps.