The Light Cannon is a great dive light, and I've used them for years. I ocassionally use it as a focus light, and it works ok for this purpose. Being an HID light, it has a blue cast to the light. I would not go so far as to say it is anywhere close to sunlight. If you stick to very fast shutter speeds (1/250+) you should be able to minimize the blue in your photos. I've had good results with it, but am not totally happy it.
The Light Cannon comes with a couple of plastic difusers and you will want to use one or two of these to spread out the beam as a focus light.
I don't use the recharger pack, but 8 rechargeable C cells. If I am using it as a focus light I don't use the highest density cells because they make the light really heavy. Still, you should be able to get about 90 - 120 minutes of light from it.
As a flashlight, it's very good for murky waters such as the Pacific Northwest, but I find it overkill in clear water. It's a great deal at < $200 but don't get it grey market or you may have trouble getting it repaired. UK is pretty good about service though.
Dave
http://www.pbase.com/davehicks