To be honest, I'm much more in favor of this API because of its privacy features than performance. I think it's a little bit faster, but it has a much bigger benefit on the trust side because extensions no longer run arbitrary JavaScript in every page I visit.
It's very improbable the few popular ad blocking extensions could slide in something sinister and avoid public scrutiny for a long time. You have much more reason to be worried about your privacy from Chrome than from uBlock Origin, since Chrome and Google provably violate it.
