Question: Is a Kingston Arms federschwert worth buying?
My verdict: No, probably not.
These have not been on the market for very long, less than a year at the time of writing this article, and there are several stories of them exploding into two (or more) pieces during competition, normal sparring, and just training in general.
They are not so much cheaper than a good feder from Regenyei Armory, so you are not really saving much money – especially if it snaps and you have to buy a new sword anyway.
If you buy a training tool that has a history of snapping, then is this fair to your training partners, who might be on the receiving end of a thrust from a broken blade? You have a duty of responsibility to your training partners, which includes not stabbing them with broken blades if at all possible, so you should probably not take the risk with a training tool with this kind of history and reputation behind it.
Keith Farrell teaches HEMA professionally, often at international events (why not hire me to teach at your event?), and has an interest in coaching instructors to become better teachers.