eSATA and Firewire work with our software. The reason they are not "officially" supported by our company, is because there are complications in certain cases. For example, eSATA connections tend to backup at a much faster rate, but there are cases where they slow down a client's computer during backup. This is due to the nature of eSATA taking up more resources than a USB drive would. As you can see, we cannot claim that our software "works in the background and does not slow down your system" and support eSATA...
What I would recommend is trying the software with your setup, whether it is eSATA of Firewire. Just make sure you have the latest software version. The latest versions can always be found here:
http://support.rebit.com/forum/topic/how-do-i-reset-rebit