There is a similar product called Pitlock that uses the same basic idea, but for all the bolts on the bike. The thing you might find interesting is that they have multiple designs for the wrench to make it more difficult for potential thieves to replicate. Other than this, I've seen regular bolt-on skewers that simply use a 5-sided key instead of a hex key. There is also a quick release skewer that is locked in place while the bike sits upright and you have to turn it upside down in order to be able to release the wheels. I don't know if you know of these things but it's good to know your market when you're releasing a competing product.