Right. Then he can get started.
He'll start the video in full armor. The pseudo-Durendal - he's just referring to it as "the armor," for now, and he's avoided some of the stylistic flourishes of the pure Durendal in case anyone from his world shows up, still gunmetal grey - is more of a wearable tank than the sleek smooth skin of tinker powered armor; it adds most of a foot to his height and the same to his width. (Part of that is the sheer thickness of the plates; he can't afford reactive armor without a tinker, and so he has no choice but to use mundane metal to make up the difference. Most of it isn't.) It has no jetpack, no build-in computers, no attached weapons; none of the flourishes. It just works.
And then he can demonstrate. Lifting very heavy weights, walking around his workshop, jogging briefly in the woods outside, loading a (perfectly legal) .44 caliber handgun in spite of the loss of dexterity in his armored fingers; he places it carefully on a table, safety on, gets out of the armor, walks to the far end of his workshop, puts on leather gloves and a safety mask, shoots it in the chest six times, and steps back to observe that although the metal was scratched the armor is not noticeably dented. (He suspects the video quality is good enough that with magnification, Dragon will be able to see that, yes, bullets did impact, it wasn't a trick.)
And then he will step back, disassemble it, and reassemble it, privately careful to swap literally identical parts himself to prove their interchangeability. (This part of the video, since he expects she may end up passing it on, is fast-forwarded; it's something that would break a large fraction of tinker constructions, in his world.) Then he'll get in it again, walk over to the weights, lift them again, and put them back down, just to prove that it still works.