If we have to build it internally, that is what we are trying to avoid.
ActiveMerchant just connects your app to a gateway for cc approval and processing.
Braintree has very nice reports on transactions and it's very easy to refund a payment.
Beyond that, you are dealing with Rails after all–it's pretty easy to scaffold out some reports from your subscriber base.
If we have to build it internally, that is what we are trying to avoid.