Why would his arms be called the widowmakers if he has never actually killed anyone with them? If he has, I'd imagine plod would be interested and, if, as I suspect, they haven't, surely this is a trading standards offence - at least false marketing.
Inviting opponents to make an appointment for a 'straightner', yeah right. Me thinketh he ought to watch his back, as a person(s) will possibly visit without appointment when he least expects it, and part him from his consciousness.
The local plod knowing of his 'invite' to challengers would not likely be too interested in committing too many resources to finding his assailant(s).