I agree that the example provided in the guide appears to concern refunding twice, but it is mentioned under the Rights and Obligations section and is but one example. Notably, the Visa dispute process states that the funds must be returned to the bank within 1 day or Visa will actually carry out the return of funds.
Neither appear to specifically mandate that the customer receive the funds immediately, nor would I expect them to do so as these agreements are between members of MasterCard/Visa. I have no doubt that Monzo are complying with any requirements, as it would be foolish of them to do otherwise in a highly regulated environment.
That said, there does appear to be a difference between Monzo and other established banks according to reported experiences. It would be interesting to compare how each other bank handles it to compare, but I doubt there is a comprehensive resource covering this.
If we think about it in the context of legacy banks, and how everything is about monitizing a customer through fees and charges, why would they care if you ended up overdrawn if the charge was represented? Personally, I wouldn’t want the mental note of “that money isn’t yet safe”, I’d just prefer to know it’s spendable.
Maybe I have a different view on how easy chargebacks should be, given how frustrating it is as a merchant to have to handle unreasonable chargebacks from customers who use it as a mechanism for cancelling/because of buyer’s regret, but justify it to banks as some kind of breach of contract.
Edit: to add some examples, the last two chargebacks I handled were for less than £10. We won both cases, but the customer never contacted us outside of the chargeback process to cancel (which is really what they wanted). I can only presume they were refunded up front and their bank absorbed the cost. That isn’t a sustainable ecosystem.