After many years of using multiple devices and even servers with Archlinux installed it never broke because of an update (spoiler: I use systemd-boot instead of grub). If a system is to be used by a less experienced user, just install linux-lts Kernel instead.
Unstable does not mean it crashes/breaks often, it just means it does not guarantee to not bump to the newest upstream version and that it does not do backports. This can be a problem when using unmaintaned software that does not like using a recent python/php.
This is also great because if you find a bug in a software you can report it to upstream directly. Debian maintainers only backport severe bugs, not every one of them. It can take over a year for new features to arrive - especially painful with applications like gimp, krita, blender, etc. You can use debian-unstable of course, which is close to upstream as well.
I use a mixture of systemd-nspawn and different user logins. This is sufficient for experimentation, for actual use I try to package (makepkg) those tools to have them organized by my package manager.
Also LVM thinpools with snapshots are a great tool. You can mount a dedicated LV to each single user home to keep everything separated.