Open schematics for a PCB don't make it any harder to hide a backdoor. You're talking about devices which still have an entirely closed source SoC with all of the real complexity. The products you're repeatedly marketing here use a bunch of low end components with very poor security including lacking ongoing patches for vulnerabilities and basic standard security protections. They're falsely marketed as open but are actually closed source hardware with closed source firmware. A closed source SoC, Wi-Fi, Bluetooth, cellular, NFC, SSD, touchscreen, camera, etc. attached to a PCB with open schematics is not open hardware.