Quad9 is a third party Domain Name Server (DNS) that uses threat intelligence to protect you from visiting dangerous websites.
The TalkTalk DNS uses threat intelligence to power the Virus Alerts feature of HomeSafe / KidsSafe. KidsSafe also delivers Scam Protection and blocking of unwanted websites by category or by individual name. The TalkTalk DNS is faster and more responsive because it's physically closer to your broadband connection. To benefit from HomeSafe and KidsSafe features it's essential to use the TalkTalk DNS. But you may use a third party DNS setup in your router if you wish and Quad9 is an interesting development in DNS techniques.