Z-Wave is 915MHz, which has much better propagation and penetration characteristics than 2.4GHz ZigBee.

I had some initial troubles that were partly hardware and partly firmware related. The earlier firmware was a little shaky and I had to reconnect stuff occasionally. Then I had some issues with an outlet going bad that started to take down the network. After replacing the outlet, it's been running without a problem for at least 6 months.

I mostly use it for scheduling things to turn on and off and voice control of my living room light. It's nice to tell Google to dim the lights when you sit down to watch a movie.