When comparing Haiku vs Guix, the Slant community recommends Guix for most people. In the question“What are the best operating systems for advanced users?” Guix is ranked 6th while Haiku is ranked 16th. The most important reason people chose Guix is:
For those with a clear focused concept of what is wanted, after building, the build can be replicated in a blink on countless machines. Both GUIX and shephard are complex but also a breath of fresh air.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
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 Stability
Pro Runs perfectly on old Hardware
Pro Atomic package management without bloated init/supervision systems
For those with a clear focused concept of what is wanted, after building, the build can be replicated in a blink on countless machines. Both GUIX and shephard are complex but also a breath of fresh air.
Pro Secure rootless installation
While the whole system can be configured using a declarative file with sufficient privileges. Users can install any package in their own local profile with a single command without root.
Pro A truly advanced operating system
Solves modern problems of software management in one concise, coherent, and fully integrated system.
Cons
Con No one uses it
It's a very niche OS that no one uses.
Con Unfinished
It's still in beta and quite unstable. Making it unsuitable for developing applications of any kind.
Con Language support is terrible

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.
Con UI quite different to other OSes
Con Not for newbies, neither for seasoned professionals, unless raging against conformity with artful purpose
