The cost, obviously... it is free :) Actually, I like how simple Invoice Ninja is to use and that it is web based. I can invoice clients from anywhere and they can easily pay through the email that they are sent.

The easy user friendly interface. Everything I need to do invoicing is right there, just a click away. It is incredibly fast. Once you're set up, you can edit invoices, add items, send invoices, enter payments, send receipts etc, with just a few clicks.

I have been using Invoice Ninja for almost a year now. Product is simple to customize and to use ! Support team answers fast.