The main difference is that our Extension Ad-Blocker works based on the existing open-sourced uBlock Origin extension blocklists. This blocking happens client-side meaning that the browser will not make requests from those blocklists.
On the other hand, R.O.B.E.R.T. blocking is DNS-based server-side filtering. These requests will get made by your browser or application and then be filtered on our VPN servers based on our curated blocklists and your custom R.O.B.E.R.T. rules. A blocked domains will return the 0.0.0.0 IP address which your browser knows as a null IP and won't load.