If you book on an international Hertz website, such as hertz.co.uk, then enter the PC 126884, you get the benefits of both no underage fee and the lower European rate that includes insurance. But the default currency may be set to USD unless you manually find a menu that converts it. And an international passport/airline ticket may be required as ID to confirm your eligibility for the international special all-inclusive rate.

With the US site, it is possible at certain airports to get a lower prepaid, noncancellable price in additon to your CDP and PC. I think that holds for international visitors as well.