I'm skeptical. There are a lot of bullshit free-energy and reactionless drive "inventors" who exhibit the same pattern. Super secretive and paranoid that the traditional scientific review process will steal their invention, will only allow third parties to experiment under very controlled conditions, etc, won't produce working patents, etc. Remember Dean Drive?

I often think they either known they're peddling something bogus and are straight out charlatans, or they actually really believed in what they have, but are too afraid of it being debunked.

Science and secrecy don't go together. A material with twice the melting point of tantalum halfnium carbide sounds like an ablative heat shield to me.