When comparing Nix vs Slax, the Slant community recommends Slax for most people. In the question“What are the best Linux distributions for desktops?” Slax is ranked 54th while Nix is ranked 75th. The most important reason people chose Slax is:
Changes you make in the configuration persist if you run from USB.
Specs
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Pros
Pro No side effects when building packages
Nix is a purely functional package management system. This means that the act of building a package does not have side effects, such as destructively updating or deleting files that may be used by other packages.
Pro Isolated development environments
Nix allows the creation of project-specific shell and build environments which are isolated from the rest of the system. These environments are defined declaratively to ensure reproducibility.
Pro Can replace docker in some places
Pro Can use multiple versions of the same package
Because of the functional approach it takes, Nix makes it easy for systems to use multiple versions of the same package simultaneously, and ensure that updating or removing a package can't break other packages.
Pro The configuration works on "All machines"
No more of the traditional: "it works on my machine". When it says reproducible, this is the real deal.
Pro Persistent changes
Changes you make in the configuration persist if you run from USB.
Pro Pretty fast to boot up
It was considerably fast to turn on when booting from cd.

Pro Modules
Standard tar archives plus some simple shell scripting produces modules that you can load dynamically into the OS for added apps and functionality.
Pro Modern desktop

Pro Small footprint
About 200mb, but with a full KDE4 environment and loads of useful apps.
Cons
Con Does not work well for services on non-NixOS systems
When using Nix with anything other than NixOS you can run into difficulties with trying to start up services. For example, you can install docker with Nix, but it won't integrate with the host system's systemd leaving you to handcraft awkward workarounds in order to start the background service that docker requires. This seems like a critical flaw when using Nix on anything that is not NixOS, and it's unfortunate because this affects many of the packages many users would be most interested in using Nix to handle.
Con Steep learning curve
Con Cannot handle filetypes that have different semantics across different versions
While the functional approach that Nix takes is great for sandboxing binary artifacts of packages, it seriously lacks any power in handling configuration files or user data. It's difficult to upgrade and downgrade files where semantics and syntax can change between versions. Especially in Debian/Ubuntu it can cause severe problems where the upgrade process blocks and the user needs to resolve the 3-way merge.
Con Feels slightly over-complicated
Con Overly complicated HDD/SSD installation
While it has a nice layout Slax's lack of an installer tool like Tinycore's just can't be justified. It seems strange that it comes built in with programs that some users may not want, yet it doesn't have an easy way to install it. Due to its heavier use of RAM, built in software, and lack of an installer its hard to choose it over TC.
Con Works slowly on old computers
Con Infrequent releases
Since Slax is maintained by only one person, releases are not that frequent. So it may take a while to get bug fixes or new features once you start using it.
