Yeah, the former is a weak phrasing of the claim. The latter is too strong, though, to be scientifically precise. Better would be "overwhelming scientific evidence that this product does not work" or "the claims of this product have been tested false across hundreds of trials."

Which is to say, we're not 100% sure it's bullshit—we can't be, in science—but we're 99.999999% sure, or so.