The HBDI is a 120-question diagnostic survey. Your answers indicate your thinking style preferences. Because it is a self-analysis, most people immediately recognize their results as accurate. It identifies your preferred approach to 'emotional, analytical, structural, and strategic thinking'.
This is a complement to the MyersBriggs personality test -- it really is about your preferred styles of thinking - "right vs. left brained", in common terms.
Is it just me, or does this sound like MadScientist? Dr. Prof. Herrmann's latest plan for WorldDomination?
I dunno, but the phrase "Because it is a self-analysis, most people immediately recognize their results as accurate" sounds too much like the observation made by the subjects of tests showing astrology is bunk - hand 20 people an "individually prepared" horoscope, and they find it accurate. Then let them see the report given the rest of the group - which is the same as theirs. People are too prone to rationalize any set of observations as matching them, as long as it has some common strengths and weaknesses.
Good point, and if that were the only claimed support for their system, that would be awfully weak. Presumably they claim other kinds of support.
Consider the flip side, though, if some other system produced results that most people rejected as inaccurate about themselves, that would probably be suspicious in a different sense. Myers-Briggs, Minnesota Multiphasic, etc, for the most part don't astonish people.
There's of course the possibility that those Jungian-derived systems aren't actually any better than cloud watching and astrology, despite claims of statistical evidence from factor analysis etc. In which case we don't have really any strong systems remaining.