I’ve heard the following rule of thumb:
Your bank has an existing customer relationship with you, so they have more of an incentive to make you a good deal on currency conversion, lest you pack up and leave.
The ATM operator’s relationship with you is literally transactional. They don’t give a crap who you are and even less of a crap once the ATM dispenses the money.
Thus, your bank is less likely to fleece you than the ATM operator, so you’re better off leaving the conversion to your bank.
I’d apologize to the viewers that the show has been so dull. I’d probably blame the writers, they obviously hired utter hacks.