I have booked Costco a non Costco trips with Covermore. Other than cost difference 6.5% vs 5% the emergency evacuation is only $500,000 when booked direct for a non Costco booking.
I have fortunately only filed one claim. For an extra day in Athens last year. It was just over $500 and was easy to file and paid promptly.
Our friends traveling with us also had no problem with their claim.