I'm intrigued as to how these company's can accept money on behalf of others, I've had a little experience of setting up an on-line payment facility and obtaining a merchant ID etc.
The last thing you want to tell a bank is that your accepting payments on behalf of someone else.... they would have a fit trust me, I tried
I see they are charging 3.4% +20p per transaction, this sounds about right from what I remember, so I'd think they are making nothing on the financial side of it, just the monthly subscriptions.
Only problem I can see is that a good many older people wont use the web to pay.
One option I've considered is leaving the customer with a card and asking them to call us and make the payment over the phone, still a proper pain in the backside though.