My assessment is this: if the probability that he's telling the truth is fat tailed enough (say roughly above 5%), then that's enough to justify being extremely interested in what he has to say. But the #1 thing that makes me doubt his claims meet this threshold is that he claims the craft he worked on violated the known laws of thermodynamics, which sends this probability to a mere epsilon over 0%.
(Since how often are known laws of physics "changed", as opposed to being merely "extended")?