Looking back, I think each prototype has takes 3 to 4 months of  'full-time' development; say about 600 hours. Unfortunately, in relation to time resource, this is not the biggest surprise. As I have developed each prototype, I have made significant progress: each one confirms to me at least, that this is a really viable concept and that keeps me going. Here's the rub though; 600 hours for each prototype is one thing but I've built at least five of them and the idea is still what I would call 'in development'. (That's a year and a half of full-time hours, which have spanned about the last five years.)

The greatest risk I believe is not that I'm the only one who really believes in the idea at the moment. I think I'm pragmatic about the effort involved in  developing the idea and its pros and cons. (After 3000 hours in a shed, I could do with an excuse to pack it in.)  I am still quite confident that it is practical - the last prototype gave me a good feeling about that. But, as an inventor, casting my eye over various novel products and markets, I sense that a greater risk than my ergonomic bike being seen by peers as of no practical benefit, is that it may have no commercial impact. I'm not looking for excuses; I just think that inventing a better machine may not guarantee that it will sell. Its almost a reflex response to inventors and invention, "Invent a better mouse trap and they'll knock down your door". Or, "invent a better bicycle and its bound to be a success", to paraphrase someone I corresponded with. I'm not sure I'm convinced about that.