This light was briefly listed at Lightinthebox.com for $3.99. I ordered at that time, but I'm not sure if this was either a pricing error, or a limited promotional pricing, as the price on this light was quickly raised to $39.99. If this was a pricing error, I'm impressed that LITB would honor the sale and ship the light rather than process as a refund after not shipping.
LITB also has what appears to be the exact same light under multiple listings with wildly varying specs, ranging from listing it as a 7x emitter light, to being a 2x 26650 light, and with prices from $29.99 to $44.99, or for $79.99 as a kit with batteries and charger.
This light is very well sealed. This light has double O-Rings at both ends of the battery tube, and has a sealed magnetic switch. The Glass lens at the bezel appears to be very rugged, and is secured with a thick O-ring. I am confident that this light would function as intended, for diving/underwater use, without any leakage issues.
The switch works well, but is only OFF/ON; there are no modes or stepless adjustment as described in the product listing. (This is a feature to me, I prefer the single-mode operation.)
The light has 3x XM-L emitters, which are very cool white, much cooler than my XM-L U2 EDC.
The emitters are very gently driven, with only about .5A being delivered from 2x 18650s. As this is a dive light, intended to be used underwater, heat shouldn't have been a concern. This does mean I should get plenty of runtime from freshly charged cells though. The heatsinking does seem to be effective on this host, as the head/body do warm up after being left tailstanding for several minutes.
The light has a parasitic drain of about .23mA (as measured by my cheap DMM) when powered off.
OD of head is about 43mm, overall length ~29cm.
Longer protected Sanyo protected cells fit, but just barely. I would expect to use this light primarily with unprotected cells.
The light has a long dive-style lanyard attached.
A couple of minor issues to report with the light:
The reflector has some defects, and there was a deep scratch on the inside of the lens. Fortunately, the scratch is not over an emitter, so it doesn't affect the beam.
As appears to be normal in budget lights, the threads on the battery tube are machined off-center, resulting in square-cut on one side, triangular on the opposite.
I had ordered two of these lights at the reduced price, and this is the first to arrive. I'm still awaiting the arrival of the second light, but until it arrives, I do not intend to tear this light down further. I intend to replace the emitters on one of these with XP-sized UV emitters to make a waterproof UV-triple. I will keep one of the two unmodified as I like the idea of having a light than can be used in the lake/pool, etc. without worrying about water damage. Once I have the second on hand, I'll do a tear-down and report back with the mod potential of these lights.
I don't own any other dive lights to compare against or base my opinions on, and I don't know what you would expect to spend on a comparable dive light, so I'm making these statements per my opinions compared against my normal budget LED lights:
For $4, I am VERY HAPPY with this light. Of course, you can't compare this to anything else, as buying the emitters alone would cost more than this entire light. It's waterproof, and light comes out of the end. Not much more you could want for the price.
For $40, I would be disappointed. This light should be priced somewhere near the middle. I would expect better machining, cleaner reflector, and more power for the full-priced light. If you absolutely need a dive light, and can't find anything better, buy the $30-listed version instead.