As a test I bought me a small videolight at Banggood, one of my preferred suppliers from China. The light itself was quite cheap. I needed only an extra battery to be able to use it every dive and some mounting gear for the camera baseplate I created earlier. (the one that holds a Canon G12 and an action camera)
The lamp has a good spread but is only 300 lumen. Batteries last about 3 dives, the way I use it. In a continued burn it probably lasts about 1:30 hours. This is more than enough for normal use. The light also has a full-half-strobe function. You will not be able to use those settings for anything else than showing off the light.
So with all the limitations what is it good for? Well: macro and anything closer than 50 cm. The light is useful on deeper dives as well, as it helps you adding red to the subjects you are videoing. In the advertised use you see the light attached to an action camera, directly under or over the camera. That is probably the worst way to add light to your video. Be sure to spend a bit more on your light setup and add arms. The o-ring is a specially made rubber band, to be able to accommodate for the corners. I had serious doubts about the concept and I asked for a spare. The first dives in Holland went ok, with me cleaning and lubricating the ring every time I open the light. Going deeper than I normally do on my Dutch dives probably made this achilles-heel part fail.
So much for the review… I used this light on my Maldives trip and it drowned. I am not sure about the cause, but I think it must have been a defective or dirty o-ring. The light drowned on the 7th or 8th dive in the Maldives. It started flickering when I was at 20 meters, I tried to shut it down, but the electronics were already fried… and the switch stopped working. I didn’t abort my dive, and the light continued to function up to half an hour, when the battery finally gave up. This was the end of the light.