They're using connect, so they're a marketplace (accepting payments on behalf of customers for their customers, and taking a cut). Not sure if any of these support that model (pretty sure Paypal doesn't).
Yes, this was a big selling point for us, we are a SaaS/Marketplace for martial arts academies and part of our business models also rely on transaction fees we get from the payment integration.
We are attempting to support mollie also to enter the dutch market but we are only 2 people writing the code here. :(
