WRT NixOS: 1. There might be slightly more convenience for the desktop user because installing applications in their user environment doesn't require root perm

WRT NixOS: 1. There might be slightly more convenience for the desktop user because installing applications in their user environment doesn't require root permission. You can set the system to a full Gnome with it's networking/wifi configuration if you like that sort of thing, but understandably it's less popular and minimalism is en vogue. 2. There is no global equivalent to Gentoo's USE flags, however most derivations follow conventions and expose comparable options with sensible defaults. These are largely easy to override. You usually lose the benefit of the large cache of binary builds so the culture of micromanaging all the options is not as prominent as in Gentoo. E.g. removing X11 support because you're not using it on a server might result in the need to locally build a lot of packages, some of them slow, and hence most don't bother with this level of "optimization." The single configuration file and rebuilding the whole system with one command (that actually runs quickly and is easily rolled back) is what caused me to finally leave Gentoo behind. I had way too much manual intervention with an almost vanilla Gentoo configuration when performing upgrades (e.g. newer profiles, but sometimes just a package update). I'm not sure if NixOS is resilient enough to allow such things as system-wide ABI changes (such as the last Gentoo profile bump) but I suspect it is, and it's mission is to provide a seamless user experience when rebuilding. Should a rebuild fail, it's not activated so you're not stuck with a partially working environment.