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 ROBERT 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.
In the future, the extension blockers will also be merged into ROBERT so that the desktop, mobile and browser clients will all have the same blocking behavior and rules.