The customer support team seems to answer your questions in the absolute least amount of words possible. Nothing like compared to Hubspot's outstanding customer service where they're always happy to hear from you, and use descriptive words / detail in their answers.
The settings, and some of the day-to-day uses can definitely get clunky. For instance, constant auto-fill from the last edited description as opposed to saving a primary description template.
Having to explain "click the approve button" "then click the pay now button" on quotes as opposed to this info being provided by invoice ninja simply on quote pages
Quotes/invoices that are expired simply reject the customer's payment instead of telling them why, or letting me know someone is trying to pay
evereytime a new line item is entered it, it gets saved. After ~6 mo of daily use with multiple team members, I had to manually delete ~400 line items because they were clogging up our drop down choices - yet slightly different than the original (pertaining to the customer's needs) yet, they are auto saved every single time.
When creating a new client to quote, they must first be quoted before the quotes tab appears under them, and allows you to quickly quote them using the "new quote" shortcut whereas the invoices tab is always there
I haven't found a way to be notified of a client's credit's they have while creating a new invoice, so this must be manually checked each time.
it would be nice to be able to put notes about a client and have them show up each time you are creating a new invoice / quote. (i understand this one may be possible, im just not aware of it)
Practice practice practice. Also, pay VERY close attention to your quotes before sending as Invoice Ninja does the auto-fill on the line items and uses the last description used (from ANY team member)