I purchased this reading light (Energizer) and found it would not clip securely to the Kobo (hard plastic against hard plastic slippage). The clip does have a tiny piece of rubber on the tips but they don't touch the plastic and they are not big enough to work. So, what I did is take a piece of bicycle inner tube and cut in the shape of both sides of the clip, contact cement and voila, a secure clip on reading light.
The moral of the story is that this clip didn't work for me out of the box and some retrofitting was required.
Now my wife doesn't complain about the light being on when I'm still reading and she wants to go to sleep!