Big props to Madvapes for posting the results of this study:
They test a 24 mg liquid with the BTB indicator kit and with a pH meter. Only criticism is that they are claiming more precision (4 significant figures) than they can, since the acid is 0.17 N (2 significant figures). But they do show that the kit when used properly does give quite reasonable results.
I had nothing to do with this study, which is good, since it means vendors are starting to take the initiative. Kudos, Madvapes!!