I have a tuxedo machine. Their support is great. The “pre installed os is bad” people have no idea what they are talking about. TuxedoOS is a Kubuntu slightly modified to include their branding (wallpapers, etc) and a couple of drivers, plus their tuxedo-center app (which you can remove if you want).
Nothing will stop you from installing any other os and if you want to come back to the original OS, you can use their WebFAI and reinstall the way they did it at the factory (or pick another os from the list).
Their hardware is fine, I have a system76 machine as well and they are comparable in every aspect, considering all of them use “generic” hardware.
I’d personally go for it if it works for you.
Good luck!
Also, apps on modern Android are mostly sandboxed so they wouldn’t be able to “block” your phone on their own unfortunately. You could have one that You make/install that could do “things” but you’d be really limited without root access to your phone.
As for the phone locking when you plug it, you can make an app that detects when the phone is being charged. What I don’t remember is if you can force-lock your phone from user space Android-provided APIs. Keeping it on while plugged is possible by checking the appropriate checkbox in the developer settings “keep screen on when plugged”.