It's worth knowing, same as your height and weight.
This gives a very close idea, I'd say +/- 3 points. It is context-free so has nothing to do with education, just pure mental horsepower. Give it a try. You will either be humbled and hate yourself for being an overachiever - or hate yourself for being an underachiever. No, not really. Many will figure they had themselves pegged correctly.
Speed counts, of course. No allowances for slower thinkers or "disabilities" because it is not a test of knowledge or operations. I came out 123 which I think is about right.