Just be very careful of the vendors you buy the keychain cameras from. While the cameras all look the same, quality varies widely from vendor to vendor. There is a very small number of eBay vendors for those cameras that are truly reliable and will deliver a quality product.
There is a great thread on an R/C board with information on those cameras, including reliable eBay sources for a true HD version around $40 bucks. I'd be happy to provide links/vendor names/etc. for those interested.