A major benefit I’m already getting (and I really hope continues when Mondo is a real bank™) is no charge on international usage and withdrawals. I pay my rent in cash in New Taiwanese Dollars 
, so I was paying some pretty hefty fees. Also I can use my card casually for smaller purchases without worrying about flat fees per transaction.
This is the sorry state of the competition. tl;dr, mostly 2-3% “foreign transaction fee” + a flat fee of £1-2 per transaction, and in many cases the non-sterling fee and withdrawal fee are combined for withdrawals abroad.