Demanding "Proof" is an avoidance tactic often used by those who don't want to look at the evidence.
Can we "prove" that Menard is a conman via convictions in court for that very accusation? No, we can't.
But we can point to evidence that supports the conclusion that he's a conman. All evidence and all conclusions are open to challenge, and that is legitimate. But demanding one and only one type of evidence, while ignoring all others, isn't useful.
We do have lots of evidence that FOTL in general is fundamentally incorrect: Every time we can see that it has been tested in the venues where such tests really matter (police interactions and court cases), it has demonstrably failed.
We know, despite all that, that Menard, and others of his ilk, continue to ply their wares, in full knowledge that they've failed as discussed above. That's evidence of their fraudulent intent.
Now, Menard has claimed that he has lots of "evidence" that this works by "keeping people out of court in the first place". However, that evidence exists only in Menard's mind - it's pure hearsay, backed up literally by nothing more than his word. He actively refuses to provide anything more than that.
So, we have clear cut positive evidence of FOTL's failures, clear cut positive evidence of Menard's continuing to sell his FOTL schemes, and only hearsay evidence from Menard himself as to FOTL's successes. The conclusion we reach, as reasonable people, is that Menard is a conman.
So, were he willing to substantiate his claims to FOTL successes, we'd re-visit that conclusion. But at this point, the reasonable provisional conclusion is that he's a conman.
If that's not enough for your friend, well, that's his life; but if and when Menard walks away with his money, he'd better expect us to say we told him so, because we will.