A shared family Windows or Mac is where browser extensions die. The teenager uses another browser, a USB stick, or the admin password. Sigma Vision is for that computer: system-level detection and lockout, not a Chrome store plugin.
It is not Bark (phones). It is not a full Qustodio suite. Parents who need texts monitored still need a phone product. Parents who need the family PC to stop are here.
Walkthrough: set up parental controls on a shared computer. Use a standard (non-admin) account for the child.