This is not a SFW instance. NSFW communities will be tagged, and efforts will be made to keep SFW communities clean, but proceed at your own comfort level.
tl;dr Try it at https://trynix.dev. Click hello, or python 3.6.2 from 2017, or two eras of hello at once, or a package that exists in no public cache. A Linux machine boots in the tab and you get a shell with those Nix packages on PATH.
This is really cool! I’m surprised how fast it boots on my phone.