Not bold, just truthful. All one has to do is look at the Aquamira site. According to their site, the tablets qualify as “the safest solution on the market”. No such claim is made for the drops and no EPA registration is listed (unlike the tablets). What is clear is that the drops have not been registered with the EPA (unlike the tablets) and, as such, their efficacy for killing the nasties to EPA requirements is unproven. As such, why trust an unproven product that is not marketed for backpackers' uses? That is not a risk that I am willing to take given the plethora of reasonable alternatives available. I don't mind people buying the liquid, but only as long as their eyes are wide open to its limitations.
As for the 13 year old study, I don't think it stands for the proposition proffered. That was done with respect to Carnebon 200 and Aspetrol separately. Are either of those actually the mixed liquid? Secondly, you may want to review the conclusions as both of those failed in killing cysts in half of the tests. Also note, that was only with respect to cysts and not other nasties. The report says it is to be submitted to both the EPA and CAL EPA. So why wasn't registration successful?