Concept/Innovative : 0.9 - This is one of the best invoice app. This app is made in such a way that it can be used by anyone from freelancers, small business units to giant companies!
Usability: 0.8 - Application flow is very smooth. It is following all the apple guidelines. But can be understood only by specific category of users.
Functionality/Correctness : 1.0 - No issues found
User Interface : 0.9 - Very good. All controls are used in very efficient way. Many controls can make application look complicated but this app is an exception!
Performance : 1.0 - Near to best. When you download this app, you get what you want without any trouble if you are one of those specific category users. And even if you are not amongst them you can give it a try as I did! And I loved it.