I like that this app allows you to download your PDFs as well, so when it's time for payroll or tax purposes they are ready whenever needed! It can be hard at times navigating between apps in order of how things should work together but there really isn't much else with which we would have an issue here (aside from maybe being able learn more about some features).
We use Invoice 24 primarily during our quarterly taxes/payroll period where most people file their returns electronically anyways - therefore no issues using paper copies via e-File Tax Connections vs having them send us by mail once filed through EfileTaxConnection instead since all information will already exist within these documents anyway if need arises later down the road (ease & accuracy!).