Note that the original writer who made the website popular may have stopped posting many years ago. For the core information, stick to the posts from 2007-2009. Everything else is potentially (and in most cases) a massive step down.

As for whether reading 2007-2009 era Heartiste would lead to instrumentally rational behavior, it would depend very much on your particular cognitive architecture, position in life, and so on. If you're a young, heterosexual male who values an extremely high level of intellectual and physical freedom, and you tend to have overly altruistic tendencies which harm you in the long term (thereby also decreasing your ability to help other people in the long term), then you may benefit very significantly from the content.

Keep in mind that he's more of an artist and wordsmith than an epistemic-mode thinker. Rather than pinpointing specific theories and arguments he makes, and then asking whether they're accurate descriptions of reality; instead read an expansive selection of his writing and notice the effects on your feelings, intuitions, etc.