Good morning Martyn,
I’ve used for a number of years Columbus Direct. Their website offers a direct quotation and in my case insurance for me and the family, 60 days any one trip, come to €360 pa for the four of us.
I’ve thankfully never had to make a claim, though a friend, to whom I recommended Columbus did and he said they were exemplary in their handling of it.
I cannot compare the benefits between your Amex and mine, as my card is issued in Switzerland, though the only thing my card gives over and above is CDW cover, though I’ve just seen Columbus now offers that as well. The only thing is I have to pay for the car rental with the card to qualify, and some places do not always accept Amex.
I’m curious how it compares and here is the link.