When comparing Haiku vs CRUX, the Slant community recommends Haiku for most people. In the question“What are the best operating systems for advanced users?” Haiku is ranked 13th while CRUX is ranked 16th.
Ranked in these QuestionsQuestion Ranking
Pro Very Fast
Pro Beta has been released
After about 6 years since the alpha version, beta has been released on Fri, 2018-09-28. Check here for release notes.
Pro Only need 512mb ram
Pro Runs perfectly on old Hardware
it uses the BSD ports system as package manager
Pro Very BSD/UNIX-like
Nice if you want to learn some stuff about Linux
Con No one uses it
It's a very niche OS that no one uses.
Con Small community
It is important when developing to be familiar with tools that other developers use. You can make any utility in any language you feel like, but if it's in an esoteric language that no one can read targeting a small platform that no one uses, then it was just something you did as a hobbyist, not as a developer.
This is not to say that Haiku isn't a great operating system to hack around on. Just don't delude yourself into thinking you're doing it to get familiar with tools that you need to know to be a better developer.
It's still in beta and quite unstable. Making it unsuitable for developing applications of any kind.
Con UI quite different to other OSes
You have to do everything by yourself there are no helpers!