They are not absorbing the Paypal transaction fee, which means that on top of the 5% I would still be charged the 2.6% that Paypal wants (amount vary). So, unless the service provides a payment gateway, where is that 5% coming from? That starts adding to the cost really fast.
It might not be pretty but ejunkie (http://www.e-junkie.com/ej/pricing.htm) has a fixed cost of 5 dollars. It ends up being cheaper as soon as I sell more than 10 copies of any $10 digital goods.
For something prettier than ejunkie (but with way less features), PulleyApp does a fixed price of $6 (http://pulleyapp.com/signup). The only reason I am not using PulleyApp is because I wanted different paypal email addresses (for microtransactions vs. regular one - different fees), and at some point the ability to call a backend service does matter for integration.
I don't really see why I would use a service that takes a commission and does not charge a fixed price unless they have a value added service. As it stands, there are better alternatives already that do the same thing.
The new thing in here is the DropBox and Google Drive integration, but that is not enough for me to justify using them.