I have the DRIS 500 light, and just received the DRIS 1000. These are about 8" long and run on three C cell batteries. The 500 has a brag of 400 minutes and the 1000 claims 320mins.
I have not had a chance to dive the 1000 yet, but will talk to it in comparison to the DRIS 500.
This twist-on light is of comparable size to the DRIS 500. The light twists on easier than does the 500, and it has a larger knurled segment on which to get a good grip. The head is the same size as the 500, and only the tapered segment from the barrel to the head has been extended. The 1000 is about 1/2 inch longer than the 500.
DRIS has, as usual, been on top of keeping us informed and producing good products. I now have my two cave backup lights.
Given that the 500 is, in my opinion, too bright for night dives, I reason that the 1000 will wash out everything badly. The 500 did not work for photography, as it caused a hot-spot white-out in pictures, and I assume the 1000 will be worse. I would bring either dive light on a night dive as an emergency signaling device, because it is so bright, but would have a softer, less luminous light for my critter-watcher.
Here is a size comparison of the DRIS 500 and the DRIS 1000:
And here is a shot of the two lights on the ceiling of a very well-lit room: