Co-Founder here - Security and privacy are one of our highest priorities. Our encryption, storage and transfer policies are as good as you'd expect with any other provider dealing with sensitive information (banking, contracts, etc).
CC'ing the bills is a convenience we provide since most companies already receive their invoices by PDF via email (or by snail mail), we also support direct upload by the firm or by the customer. No human eyes, except the customers, see the data unless absolutely necessary, and that access is limited to select, named, screened individuals.
We currently do not aggregate data or share data in any way. There may come a time where we provide insights into billing practices or fraudulent activities in aggregate, but that is a ways out.
While we agree that incremental billing (in 6 minute increments) [edit] is a pain for both lawyers and customers[/edit], it's not a model that can be wholly abandoned. However, we do plan to be in the forefront of fixing the headache and process.