When comparing Tails vs Nix os , the Slant community recommends Tails for most people. In the question“What is the most secure Linux distro?” Tails is ranked 1st while Nix os is ranked 6th.
Ranked in these QuestionsQuestion Ranking
Pro Privacy focused
Pro Has TOR built-in
Use the Internet anonymously and circumvent censorship; all connections to the Internet are forced to go through the Tor network.
Pro Upgrading the system is extremely reliable
Since NixOS stores all its packages in isolation from each other in
/nix/store and because of the declarative configuration model, upgrading NoxOS systems is extremely reliable. Furthermore, it gives you the ability to roll back upgrades.
Pro Extremely reproducible state of installation
Every package in your system is generated from a configuration file. This makes it very easy to reproduce that environment. Just copy the config file into a new machine and it's done.
Pro Versatile snapshot system
You can use and test snapshots without rebooting. Booting into snapshots or test configurations is possible without risking the system's stability.
Pro Great for Haskell development
It has all of hackage in it's package manager (which is confusingly named "nix" as well) due to being based around hashing and allowing you to compile in a sort of virtual machine (really just changing the PATH variable temporarily) it solves many of the versioning problems that you commonly have with cabal. Here's a tutorial (there's many others as well) http://www.cse.chalmers.se/~bernardy/nix.html.
Also I should note that you can use the package manager a la carte on Mac and most any linux distro.
Pro Has docker like system built in
Pro Allows parallel configurations for multiple projects
As everything is isolated, you can have on the same machine multiple configurations to meet project requirements that would be mutually exclusive on other OSes.
Con Not for daily use
Tails is a privacy focused Linux distro. The updates that you will receive are only for improving privacy and not for improving user experience.
Con Saved states are not present for security
For security reasons, saved states are not supported in Tails. Files can be stored in a separate, persistent volume which must be accessed with a root password. Personal settings (e.g. -- keyboard layout, window settings, etc.) are not saved persistently across reboots. This can be a hindrance for anyone not using English as their language, or not using a QWERTY keyboard layout.
Con You can't install it to a hard drive
Con Slow internet
Tails uses the TOR network and as a result the internet on your computer will be very slow.
Con The configuration language is hard to figure out
For good reason. It's a purely functional language. However not even close to bash.