So far (2 weeks) the R6400 has been great. Its signal is much stronger and more reliable than the Verizon router it replaced, although it still needs to be placed somewhere central to be able to use WiFi reliably anywhere in the house. Setup was clear and easy - good written instructions provided, and while it doesn't have the most user-friendly interface, it definitely doesn't have the worst either. Very nice touch: you can turn off all but one of the very bright lights on the router.
We have been using this router model for a while now and when our old one went out and we purchased this one, we were pleased to see that the range had improved, the setup was easy, and overall we are a happy business client.