I've bought two.
The first looks EXACTLY like the "muvi" cameras, but is unbranded and only cost me £16 on
ebay. I made a bracket for my handlebars out of an old reflector and some cable ties. The image quality is ok, and the battery lasts about 45 minutes on a full charge.
However, that wasn't long enough for my commute, so I bought another camera that cost about £25. I made a bracket for handlebars for this one too, (although it comes with a helmet attachment in the box). using two internal AAA batteries it only did about 25 minutes, so I took it apart, added a jack socket, and made a battery case that takes 4 AA batteries that I can strap to my crossbar. Now it runs for about 4 hours on fully charged batteries.
If you want me to send you pictures and more details, drop me a line.