I have been using Kashflow since February 2015, before that my accounts were kept in Excel spreadsheets. Setting up the invoice and purchase order templates were not as easy as they could have been, but didn't present too much of a problem, and once they are set up how you want them you won't need to go back to them.
You can create quotes and tag them with their status, won, lost, draft etc. Quotes can be converted to invoices with the touch of a button, saving time. And credit notes raised in a similar fashion.
Purchase orders can also be raised and the system keeps track of your bank balance too. The Dashboard gives you an overview of how much is in your bank account, how much you owe to suppliers and how much is owed to you.