I had the opposite experience because I want to run a lot of software in random repos.

I can make a nix-shell for each project but then every nix upgrade was forcing me to go through a lengthy reinstall + wrecking compatibility sometimes.

Not to mention the amount of derivations I had to write myself just to use latest packages.

Using things like virtualenv instead of nix-shell can fix the general instability, but packaging is too big of a problem.

I went back to Arch.