The lights are much smaller than I expected, they're only about 2cm square. This makes them a lot lighter and smaller than most other lights on the market and I just pop them in my pocket when I leave my bike.
I know other knog lights have been known to fall off the bike, due to their unique rubber band hoop and clip. These have a plastic/metal hook which seems much sturdier than the simplier rubber band hoop, and the lights seem very securely attached.
Also you don't have to worry about brackets and you can hook them around any part of the bike.
The lights themselves are really really bright, I feel much safer using them than the bulky lights on the market that fade and run out of power after a month or so.
I know some people have found knog lights seem to turn themselves on by themselves but you have to hold the on button for about 2 seconds to turn these on, and I haven't had a problem with them miraculously turning on.
The rechargeable feature is excellent, purchasing batteries for other bike lights is a hassle.
Overall a great product and I think they are a very reasonable price!