I really like the idea and the product itself. The main issue for me is that it doesn't offer any kind of integrations like Zapier, Pabbly and Make (or at least webhooks). I think this is something that needs to be a part of the core features since I'm sure many people would like to send those invoices further to their Invoicing tools, internal repositories, forward to their accountants based on certain criteria etc.
I'll keep it for a while to see whether this will change. If yes, than great. If no, then too bad since I think it will be too closed as a system and will never reach its full potential.