Well worth buying if you can pick them up for £20 or so on ebay. They are a bit expensive brand new. They also have a temperature sensor included which works with Alexa. Now my kitchen light just comes on by itself whenever I go in there and its after sunset and turns off by itself when I leave. You'll need to add Web Core to your Smart Things interface if you want to do stuff like that yourself.
Very pleased with the motion sensor that I have set up in conjunction with door sensors and smart socket to manage household lamps when going out or coming home. Also receive alerts if motion is detected whilst out
Appears to be reliable. No false alarms as yet and lighting works a treat.