Guillaume-Blue-Turtle bunq's Travel card and Metalcard are real creditcards. Let there be no doubt about that. They are exactly the same in acceptance as any other Mastercard creditcard. It is not a prepaid or debit card. However, bunq build something nice; although the card is accepted like a creditcard it behaves like a debitcard (but only for the consumer, merchants cannot see this!).
Basically, the card has a flexible spending limit, this limit is exactly equal to your balance on the connected IBAN. When you do not have sufficient funds a payment will be rejected. Paying in instalments is only possible when the merchant offers this. bunq doesn't offer this, as every transaction is immediately settled with the balance in your IBAN.