My experience so far with Monzo in Sri Lanka:
The issues is that at the transaction moment it says one exchange rate which is not final then the final one is different. In my case always lower from 188.5 to 185.5.
I think somehow should be introduced a feature to know the exact exchange rate before cashing out.
Also for some reason some banks seems to charge a fee to cash out.
Banks without any fees:
Nations thrust bank
SampathBank - SET ATM
Banks with fees:
Ceylon - 300LKR
Commercial - 300LKR
Hatton commercial -200LKR