I interviewed a full day at a mathematical hedge fund. Not exactly brainteasers, rather a barrage of good, solid math and stats questions. Such a day is exhilarating (like skiing the Olympics) but truly exhausting, and only partially related to whether one gets an offer.
My advice to anyone doing this would be to give up the last 10% of performance in order to focus some on contextual awareness. These puzzles are a form of pre-surgical anesthesia, before they ask the real questions. You need the spare cycles at the end of a long day to imagine what casual conversation might really be exploring, how other applicants might misread the subtext, what mistakes in previous hiring they're trying not to repeat. One could be a genius trained seal, by buying into the brainteaser game, and miss the broader question of how you will fit into their firm. One who sees broader contexts ends up running places; don't make it clear that's not you.
My advice to anyone doing this would be to give up the last 10% of performance in order to focus some on contextual awareness. These puzzles are a form of pre-surgical anesthesia, before they ask the real questions. You need the spare cycles at the end of a long day to imagine what casual conversation might really be exploring, how other applicants might misread the subtext, what mistakes in previous hiring they're trying not to repeat. One could be a genius trained seal, by buying into the brainteaser game, and miss the broader question of how you will fit into their firm. One who sees broader contexts ends up running places; don't make it clear that's not you.