I have had a lot a success with Zigbee for lighting but I have noticed a small issue. If I keep pushing all on then all off rapidly it overwhelms something and stops working until it catches up. This is a really minor issue and I do tell my customers to simply wait a few seconds between presses. In all reality this is never done expect to demo the lights and the system can take a few on/offs before it stops working.
This issue does not exist with the Lutron bridge Caseta or RA2 so it is probably related to the Zigbee module.