Linux's "security through obscurity"
I lost braincells reading this. The entire point of open source software is to have it visible and auditable, aka the exact opposite of security through obscurity.
If you want to bash OS's for relying on STO, go after iOS and Windows. Those OS's, being closed source, are the ones relying on it
A quick search for open source robot mowers pointed me to this: https://openmower.de/
As for Oomwoo, they're still working on assembly instructions, so I wouldn't immediately jump in unless you're fine with a lot of tinkering. Also, it looks like right now they're only considering parts kits, not fully assembled bots, and that seems to be a future add.
I personally still think it's cool and will be keeping an eye on it