My understanding is the main problem here is that the machines became effectively unbootable. This wouldn't happen in nixos because if setup properly all core system files are handled by nixos itself. That being said obviously it depends on how a user manages their system.

Nixos wouldn't have had any issues, it maintains state information based on configuration and you can choose to load an older boot image during bootloader. Other immutable distros it depends on how they work

When I bought it, it was 40 bucks. They're also full of functionality like having a "smart" mode which doesn't kill power to the bulb on off (good for lights with color adjustment for day/night) and zigbee pairing (light switch connects directly to zigbee bulbs)

If they're all on the same line you should only have to bypass one, but I'm no electrician I just hooked it up to a double light in my bathroom. The bypass was recommended in the inovelli document that came with the switch

I got these, the blues are zigbee, red is zwave. I also have no neutral and they work fine, though you might need an aeotec bypass if you lights flicker with no neutral https://www.amazon.com/gp/aw/d/B0BG329SH3?psc=1&ref=ppx_pop_mob_b_asin_title