The light itself is quite a looker being aluminium on the front and sides and silicone and polycarbonate housing for the rear.
The locking mechanism is a rather clever affair and reminds me of the double clasps you sometimes see on watches. It is very easy to work and more importantly the rubber is very heavy duty and looks as if it could take a fair bit of abuse.
The light is waterproof and at 39g you will hardly notice it is there in terms of weight.
The other great thing about this light is that it is very small. I have placed a £2 coin so you can judge how big it is.
On the underside of the light a small USB flap can be flicked open and it can be plugged straight in to any UBS port. A charging light tells you if it is charging and it goes green when it has been fully charged. I left it plugged into a PC at work for a couple of hours and it was fully charged by the time I got back.
The light had four LED's and continued presses of the rear on and off button cycles you through the various lighting options. There are a few different flashing modes and on one of these settings the burn time will be 50 hours. If just on a steady light the burn time will be 3 hours. (I always have rear lights flashing so this is good news for me).
This light is more of a to be seen light but it puts out 44 lumens and is visible for 800m. I certainly thought it brighter than either of the rear CatEye lights I own. (I also think that the build quality of this Knog light makes my CatEye lights seem like a child's toy).
I pondered quite a bit about whether or not I was going to buy this light while drinking a cup of coffee and I am very glad that I ended up buying them. The first time I will use them in earnest is going to be Friday night / Saturday morning when I cycle from London to Southend. I will let you know how I get on with them after I have done that ride but if you are in the market for some rear LED lights, you could a lot worse than give these a go!