I would never go so far as to say IQ tests are useless. A properly administered WAIS-R (or whatever its current name is) not only gives a full scale IQ - a single number - but also verbal IQ and spatial IQ, as well as specific subtests. Not only that, but the test is administered one-to-one by a trained professional. Their written report should not only state all of the above scores, but whether the individual showed motivation, fatigue, frustration, distractibility, and so on. In specific cases, the tester may also "test the limits," for instance by giving additional time, to see if the test subject can perform the test when given adequate time.
All this information is useful in diagnosing mental, psychological, and particularly educational issues, and even neuropsychological issues such as specific brain damage in an accident or stroke. In autism assessment, the difference between the subtests can be very useful, and is usually quite a bit larger than in a typical NT subject.
This is a far cry from an online only test, and I have very little respect for them. That said, they will give a gross ball park estimate, along the lines of WAY bad scorer, average scorer, pretty good scorer. You could use this for a basis to get professionally tested, but you definitely should not give it much more credence than that.
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