Yup, absolutely his idea inspired me. It was the single creative element that made me realise that I can make invoicing a bit better than the other folks.
Besides a history and autocompletion... I can't think of anything else to improve this app.
Are you planning on adding PDF export? Or, at least, something like "email this invoice"? I don't interact with my clients in person, so just the ability to print an invoice is clearly not enough to make me use your app.
Besides a history and autocompletion... I can't think of anything else to improve this app.