Have any of the major players (Geico?) signed on? Do they feel threatened by Goog Compare?
Car insurance for the major players in the U.S. has historically been about capturing users in the funnel, and making pricing information extremely opaque. This is very different from how the UK operates (see https://www.google.co.uk/compare/).
Price transparency like this is the death knell for the likes of geico, state farm...etc.