Thanks. I pushed through a test on a Mastercard debit card that has no commission and uses the mid, if anyone's interested. Numbers are against sterling.
Paid ARG700 to top up my Personal mobile account on the 10th January.
Was immediately charged at £3.22 - a rate of which matched the official rate at the time - 217.39. As per dollar blue website, 'blue dollar' rate against GBP was 430.
I checked on dolarhoy.com and that showed MEP at 376.
Refunded on the 12th by £1.32
Total effective cost is £1.90 for 700ARS. Effective FX rate is 368.
So what I was charged on Mastercard was 98% of MEP and 85.5% of Dollar Blue.
I'll probably keep using the Western Union approach day to day, but it's nice to have this as an option now. Wonder what this has done to WU's business.