In the past, I've reported on numerous companies who had too-good-to-be-true 'products' that seemed to break the laws of physics but were not actually available for testing. Almost got enough for a book by now. once I work out how not to be sued. (I've been threatened with that, and UK libel laws make it a most credible deterrent.)
Some of them had pseudonymous online supporters - there's usually just one per company - who had no admitted connection to the company but conducted remarkably shrill, aggressive and intemperate online campaigns against anyone who criticised the company, regardless of how careful that criticism was. One in particular went as far as leaving me voicemails, subscribing me to large number of mailing lists, and posting stuff of a personal (and inaccurate) nature that proved remarkably counter-productive.
All you can do is what Dave's doing now: stick to the facts, keep on asking the questions that can't (or won't) be answered, and make sure that anyone who is interested in investing in or supporting the company because they think the technology has potential can find the credible criticism and inconvenient facts that indicates otherwise. More than that, is up to them.
Shrill shills give themselves away every time they post. Campaigns to denigrate or shut down online criticism leave fingerprints over everything they touch. You can't prevent this, but you can patiently and in good faith point them out - and then get on with the rest of the stuff you do. In Dave's case, that's assembling 800+ entertaining, informative (and occasionally trying!) videos that have absolutely no agenda except the one he stands by.
Look at the opposition, laugh, sigh and move on...