UPDATE- American Express suspense his relations with Curve, You cannot now American Express Card with Curve.
I using Curve since lunch, basically is buffer card (MasterCard) which let You using any Your existing payment cards, whether they be debit or credit, Visa, MasterCard or American Express.
If You have curd card You can link Your Amex platinum to this card and everywhere then they accept MasterCard. On Amex statement You will see Curve Purchase as “CRV*xxxxx” where xxxxxx is name of the original merchant.
With Curve You can pay your HMRC tax with American Express Card, even You can pay off Your American Express card balance using curve linked to for other Master Card like Lufthansa. So You can earn extra points. You can also withdraw money from ATM and earn points.
If You apply for Blue card via this link
https://curve.page.link/vL1U You and I will get 5 GBP after first transaction. Here are most important information about fees:
Full Curve card comparison You can find at this page http://www.curve.app/en-gb/comparison