Have you ever used/considered using another rolling release? If yes, how would you compare them to Debian testing?

Also, are there any parts of Debian testing that is not rolling (i.e. OS version number or some package versions like kernel or Node.js)?

I've always used Debian since I discovered it via Knoppix (which was my first Linux distro, Cygwin was my first Unix distro), I initially used Debian unstable but downgraded to testing some years later as upgrading testing often is smoother than unstable. I've never considered even trying any other distro. Everything is rolling, except unmaintained software, that just gets removed from the distro when other faster rolling things change incompatibly.

Why 4 times daily and do you do that while you're working?

How do you deal with packages being broken until the next reboot if you do updates during the day?

I don't even update my Arch boxes that regularly and always do a reboot afterwards.

The Debian archive is updated 4 times daily, so I update my system after each Debian update. I do that no matter whether I am working or not.

Packages almost always aren't broken in Debian testing but if they were, a reboot would not fix them anyway.

I restart processes instead of rebooting (using the needrestart/needrestart-session tools). I only reboot after Linux kernel image/module updates or microcode updates, because Debian cannot yet live-update those components.