I'm biased as I'm related to the creator (he's my brother and co-founder) but this is incredibly easy to use. We've used it at Hipmob to process all our invoices (whenever a customer requests one).<p>Femi (the creator) is also super responsive so drop him a line if you have feature requests! (fomojola@ideasynthesis.com)
How would this stack up against something like Manager.io (<a href="http://www.manager.io/" rel="nofollow">http://www.manager.io/</a>) which provides the same functionality and more for free?