It is made of plastic, about 150mm long, and comes with four sets of fixings to attach it to your bike. It's a little fiddly to put the screws in, but it only takes about 5 minutes.
If you're mounting it on the back wheel, be sure to put it on the other side of the wheel from the gears; otherwise it will hit off the derailleur when it is in a low gear.
It works really well, and produces loads of continuously changing random patterns.
It has a quick release feature, so you can pop the light out of its brackets quite easily, which is a good idea, because it really does draw attention.
Once again, good value, great free delivery.