I think there's a hint in there that this is not a serious bike. If you read the website it's clearly not being sold by a proper bike retailer. I appreciate the need to emphasise safety, but maybe a polite response might be something like, "Interesting bike, but can I just tell you that in its present set up your bike is technically illegal, here's what you have to do to make it safe and legal...... blah, blah, blah.......What's your bike specifically designed for anyway?" Giving the guy three pages of agro seems a tad territorial to me.