Well, my first experience wasn't great. It says to take the back off to take out the plastic in the battery to connect it, but getting the back off was hard. Ended up prying it off with a screw driver hoping I wasn't gonna break it.
And then (probably unrelated) the switch on the side didn't work. I thought there's no point stopping now, so I pulled the cover off and found the switch wasn't well attached to the board. It would wobble back and forth, so I got some cardboard and folded it up, jammed it behind the switch to hold it in place.
It's all working great now! But not a great first impression.
I haven't used the smart switch except to try to connect it from about 10M away from the zigbee controller, through two walls. It didn't work, but I managed to get it recognised by trying a bit closer, but haven't actually done anything else with it. I'm considering buying a 5 or 8 pack and spreading them around the house to get a good network going.