The Garmin Edge 200 retails for £105 - £125 and at the moment you can get a £30 cash back from Garmin if you submit a picture of your old cycle computer and send your receipt in. A pretty good deal.
This particular version does not store maps or will give you turn by turn directions (they cost a great deal more). What it does do is provide very accurate information:
Elevation / descent
It comes with a wall charger, USB cable, a couple of handlebar mounts and lots of industrial rubber bands to attach the mount to the bars.
The mount is brilliant and stays in place and did not come lose at all under demanding conditions at the BWC. Place the device in the mount, turn and click into place and it is locked in. Simply turn the other way to take off. Very simple.
The device is very small and lightweight. The display is large and visible both day (including sunshine) and at night, due to its backlit display as seen in the picture above.
The battery lasts 14 hours so even for longer trips you shouldn't have to worry about it running out of juice. Charging can be via USB attached to a PC/Mac or via mains charger.
When turning the device on it locks on to the GPS signal very quickly. I put it to one side and unfolding my Brompton, mounted it to the handlebars and it was ready to start mapping.
One of the great features is the ability to download your rides to the Garmin Connect website and look at lots of statistics, graphs and maps of your routes. I really liked this and looking at the BWC data I can see what/where on the course I could do better next time.
As I said I really like this GPS device and as it requires no sensor or magnet attached to the wheel, there is a great deal less fuss. In the future I might upgrade to a mapping unit but for the foreseeable future, this little Edge 200 will be attached to whatever Brompton I care to take for a spin.
Please see the links on my Brompton World Championship 2012 blog entry for the Garmin Connect links for the Brompton Marathon and Brompton World Championships data.