Earlier quoted context omitted.
For me the killer feature is foreign currency transactions with no fees at the MasterCard exchange rate, both online and abroad. My "traditional" bank charges me a flat fee and a percentage for any transactions in other currencies.
I don't know what the MasterCard exchange rate is. However, someone recently told me regarding their credit card: "they give me the wholesale exchange rate, which is great". It turned out not to be so great (~1% wide market). It's good not to pay an additional fee/spread on top, but it can still be a poor deal overall.
$10000 dollars cost £7,867.91
I googled $100 USD to GBP and it comes out as: £7,859.50
Percentage difference: 0.106947%
https://www.mastercard.co.uk/en-gb/consumers/get-support/con...