Looks very interesting Dave. Can you do one thing for me, look in the lens and see how many led's it has, it's just there seems to be some confusion on t'internet.
Some claim it has a single led, while others claim it uses the Cree XR-E Q5. But that led is capable of about 200ish lumens, so it's either using 4 of them, or not using that at all.
More likely is the MC-E. That can produce over 800, depending on the bin, and tally's with the 12W claim as it runs up to 2.8 amps, so it was running at it's max rating it would need an input volatge of around 4 volts, which is spot on for a single lithium cell hot of the charger.
The problem with MC-E's is because they are quad die emitters, effectively 4 led's crammed tightly together, is they are hard to focus into a narrow beam which is generally preferred for diving because of the illuminating area on the chip. This light looks to have a decent depth reflector which should work well though.
It looks well built and the bits it comes with like the pistol grip and the diffuser lens are nice touches. I'm a bit surprised by the rubber cover around the front of the torch though as high powered LEDs worst enemy is heat and that cover will insulate the heat sink the led will be mounted on from the water. I'm sure they've thoroughly tested it though.
The price seems pretty decent, though you can get MC-E dive torches for well under £100, but they're not as well built as your Darkbuster appears to be.
Overall it looks like a good torch, I'd like to know about that led though. If you can clearly see it does it appear to have a black cross in the middle of the yellow area like the one second from the left on this pic: