The ThreatPoint Web Site checker protects accidental browsing of mature, explicit and sensitive sites. The extensions takes the active URL and passes it to the ThreatPoint content checker restAPI. The URL is parsed against a live DB of thousands of known mature, explicit and sensitive sites as well as using keyword natural language matching. If a match is found the browser is redirected away from the site to https://threatpoint.co.uk/threatpoint-content-check. 
Subscribers to the service have additional options available -personal lists (block and allow, time controls, day controls and more) - see https://threatpoint.co.uk/documentation for detail on the subscriber service.