This seems like a great alternative funding model for the web. Modern online advertising has a lot of issues (privacy, intrusiveness) but most users don't want to directly pay for the sites they browse either (i.e. the subscription model). By displaying ads controlled by the browser rather than the website, the user gets a lot more control over the ads they see (solving the privacy and intrusiveness problem), while still supporting the websites they visit without paying for them directly.

The only major problem with this funding model that I can see is that it provides no incentive for users to contribute to the websites they visit at all. They can just as easily block ads and not replace that revenue with anything, which is actually the default behavior. It's essentially moving from a web funded by advertising to a web funded by donations; and based on past experience in using donations to fund open source projects I can't really see that model working out well for anyone but large, popular websites with minimal operational costs.

Though on the other hand, Brave does eliminate a lot of the friction associated with the typical donations model. Maybe they'll be more effective at soliciting donations on behalf of websites than previous efforts have been. It's hard to know for sure.