Easy to set-up, simple interface makes it easy for our customers to set up their invoices and also receive payment reminders with all relevant information in one place. It has helped us get new clients quicker than any other system we've used before! Nothing yet - would like to try out more features but are currently happy where they're at now. We use this tool as an additional billing and accounting solution for some of our Clients (mainly B2B). The most important thing is that you can easily integrate third party applications such as Zapier or IFTTT, so you don't have to rely on your own resources.