Most dive lights use the Hall Effect. There is no physical link between the button, or in many cases ring, on the outside and the electronics on the inside. Instead the slider in this case will contain a magnet which will have and influence on a coil on the inside.
This has the head screwing down. Whether the o-ring is effective or not depends on what the o-ring is against. If it is in laying in a groove cut into a ledge then this design may be fine. Water pressure pushes against the glass compressing the o-ring which pushes back against the glass.
If it is an o-ring with the glass behind it and nothing else then it's going to leak of course. I have one dive light that has one o-ring on top of the lens (from the outside), one around the outer edge of the glass and another under the glass.
There are many different o-ring systems that work (and some that don't) :)
The main concern I would have with this light is that it would be too floody for a dive light under any conditions other than clear unlimited visibility waters. The head is only about 44 mm it looks like. I have a 52 mm head used with a MC-E and it works pretty well.
If someone buys this light a dive report would be welcome :)
Thanks for the pics. According to XTAR customer support this torch is made in XTAR's former co-factory. I asked why they separated from the manufacturer and a vague comment about quality was made.
Anyhoo, the torch probably uses the same electronics as the Xtar D01 designed for a XP-G R5 LED. The specs match the D01 and XTAR has just released an extension tube for allowing the use of a second 18650 cell. This torch obviously has a buck driver which can handle the additional voltage whereas the D06 (XM-L version) does not and can not use the extension tube. The light head design seems similar to the D01 also.
The D06 seems to be driven at 2A. I asked if it could be driven harder and they mentioned that the insides would overheat.