We haven't done it yet, but had some discussions to understand how it works. My understanding is that you send a payment file to the bank / credit card processor, not sure of the format. Then the bank pays the vendor directly via a virtual credit card. The vendor gets an email telling them they received a payment with a link to the portal for them to claim it.
Pros: It takes you out of the loop from having to maintain ACH information, and I believe transfers some of that risk to the bank. The bank maintains the payment link to the vendor. In addition (and this is the selling point) you get a rebate from the credit card processor.
Cons: Your vendors get charged a service fee for accepting a credit card transaction (making it possible for you to get a rebate). Also, the credit card processor contacts your vendor to get them to sign up.
It may be the wave of the future... I get hit up at every conference to 'just send us your vendor file and we'll tell you how many already participate', and it seems like more and more companies are going to some form of it.