It looks like a scam to me. It reminds me of the
Dean Drive. The inventor wanted to be paid up front before he would demonstrate it.
It was said Dean was afraid his invention would be stolen from him. Such fears might not have been groundless. If the invention was simple but unobvious then it could be easily reinvented.
The
interval wiper might be one example. Robert Kearns real contribution was the idea, not its implementation. The cat was out of the bag once another engineer heard of the idea.
If Dean was smart enough to invent a reactionless drive he should have been smart enough to make it impossible to cheat him.
A copy of the plans and photographs of the device in the hands of a neutral third party ahead of time should do it. Have a lawyer put a sealed package in a bank safety deposit box. If you're really paranoid do this with several different lawyers and banks.
A reactionless drive would be worth trillions eventually. Smart people would not want to cheat the inventor.
If Steorn has something real they should be willing to show everything in exchange for a contract specifying royalties. By all means take precautions.