Jane Street is big in OCaml and CompSci worlds but the only guy I know who worked there did ETF arbitrage/redemption/creation which has to be one of the most boring businesses on the street. Is it worth working there (aside from the salaries)?
Best in class engineering and internet scale problems? Nope, you aren't going to find that at any hedge fund. They are much more like small start up cultures. Speed and results are favored over a mature engineering culture and maintainable code.
Want to have the potential to make a large direct impact and make a crap load of money? Well then, a hedge fund may be a good fit.
> Best in class engineering and internet scale problems? Nope
This is mostly true apart from a few specific teams and projects. I think most passionate engineers would find the work uninspiring.
I think in general though a small company (JS has 900 employees, so I'm guessing around 50-100 devs) simply can't hyper optimize their entire engineering stack to the same extent that a large FAANG can. It's far too wasteful. And I'm talking about tooling, infra, and overall process, not just the code. Code review is the minimum any competent engineering org should be doing.
It depends what you mean by "optimizing their engineering stack". They certainly do put a lot of effort into tooling, by necessity since historically there hasn't been much available for OCaml. For an example of stuff going beyond the open source work to make OCaml usable for large projects, see https://blog.janestreet.com/putting-the-i-back-in-ide-toward...
Obviously there is a lot of infrastructure that you need at a FAANG and not at a company with a few hundred devs. But any trading company that doesn't want to pull a Knight Capital needs to make sure their software is correct and reliable (probably to a greater extent than most of a FAANG).
Apart from the OCaml compiler, everything else is fairly typical of the spectrum of roles you can find at the very large high frequency firms. And mid-sized firms are similar yet again, minus the basic research. I would say it is definitely worth working in this industry if anything above sounds interesting to you.