I was able to sign up to Flex this week, and give the transactions a go today 
Really pleased to find it’s a credit card-ish option with section 75 protection and 0% commission on foreign currency transactions!
I use YNAB for budgeting, so I was surprised to find that I couldn’t use open banking to automatically import the Flex transactions into a YNAB credit card account. I guess they won’t exist in the API until they are paid off in the main account. Which means I’ll have to manually add each transaction to an unlinked credit card account in YNAB and use the QIF statement export to reconcile. This was also raised in Flex reporting on open banking.