The bottom line here is one of trust. Each of us has to make a decision when choosing who to spend money with and a large part of that process has to be based on trust, using as much information as we can get hold of.
I'm in two minds about this seller.
There is evidence, and an open admission by him, that he has no regard for intellectual property. In my view, that's no reason, on its own, to not do business with him. After all, we all buy from Chinese manufacturers who similarly have no regard for intellectual property. The performance claims, together with the responses to queries that have been posted here, do give me cause for concern. Threatening people, who are doing nothing more than pointing out something that is blatantly unlawful, is not a good tactic when it comes to winning confidence from potential customers.
However, the final arbiter when it comes to making a decision about purchasing from any professionally run business has to come down to a personal view of all aspects of that business, from their ethical view, through the morals and professionalism of the way they respond to potential customers, to the premises they operate from.
I'd advise anyone buying from any supplier to check them out carefully, using all the tools available to a savvy internet user, and make up their own mind as to whether or not they want to risk spending their money with them. I'd also want to check the warranty provided and make sure that the company was in a position to honour any future warranty claim, bearing in mind the legal requirements for certain minimum periods of warranty cover for parts and services, as required under UK law.
Jeremy