When you return from a trip the app tells you how much money in £ you spent in that location. I might be a useful idea to calculate how much the standard bank rates are against the rate you received from Monzo and tell you how much you saved by using Monzo instead of you normal say Barclays debit card.
You already have the per transaction currency conversion, you would probably just need to track that currency rate from the major banks sell rate and average it out to get a estimate of what you saved.
Cheers
Dan.
