This is a good example, why not all devices should be connected to foreign servers. Errors can happen everywhere. But it could end badly, if some Corporations make errors and creating trouble, which would otherwise not happen.
In the case of the 3D-printer it is not that bad (except it destroys itself or even gets on fire), also you can turn it off. But imagine a smart stove top that lights up a towel (or something similar) while nobody is home.
Not, that I think that it is not useful to have something like that, but wouldn’t it be nice, if that stuff would work locally? (with the WireGuard integration in modems, the access from outside of home with the smartphone, should also be no problem for non-tech people)
Is there a guide for setting up a DMZ? I have a Nest cam for our dog (bought wayyy before Google bought them out) and use HomeKit for everything that allows it, but those devices have their own apps too so they have almost unfettered access to the net. I like having my AC on internet so I can turn it on/off when I’m not home in case I forgot to turn it on that morning (living in the PNW, so we don’t need it every day in the summer, as open windows are good enough and free), so I get home to a moderately cooled place rather than a hot box.