Choosing and using an underwater video light is, in a way, getting more complex as the choice of products available increases. A few years ago the choice was limited to a handful of very expensive HID designs...now seems that more and more manufacturers are offering some sort of LED light. That's just the point..."some sort of LED" light. The choice becomes even more involved for the photographer (like myself) who wants to take stills as well as video during the same dive, without doubling up on strobes and LED lights.
It's a personal choice but by way of guidance I will just make several points:
1) Google is your best and unbiased friend...see what's out there, check out the specs/prices/knowledge of subject shown in the manufacturer's website. Make a shortlist of possible alternative products that interest you. Don't be shy about emailing the manufacturers with any technical questions you might have.
2) Compare apples with apples...not with oranges. Compare different units of similar true power output...i.e. 4000/5000 @ THE SAME UW BEAM ANGLE (e.g. 120 degrees or 80 degrees).
3) Consider battery design and safety (and Airline regulations for carry-on or shipping in different regions).
4) Price/value for money. The days of overpriced but underperforming product is rapidly ending. A very good LED video light shouldn't cost much over $1500 these days. (compared to the $3000 HID's of several years ago).
5) Since LED is really the only way to go...how up to date is the LED emitter technology (particularly in terms of Lumen per Watt output and video desirable Chromaticity characteristics). This can vary enormously...from 160 Lumens per Watt (CREE XM-Ls) to abysmal, sub 100 Lm/W (cheap emitters). The latter is actually more common (the more emitters, the less efficient is a reasonable assumption)...even in some expensive lights currently on the market. Again, email the manufacturer about this if their website doen't give relevant specs. 250 Lumens per Watt has already been demonstrated by CREE and should be available to manufacturers in the near future. Expect 8000 Lumen compact lights to become common and affordable in the next year or two.
6) How functional is the design for real world use? Interchangable batteries? Double O-ring sealing? Field repairable? Switch ergonomics? Bouyancy characteristics?
7) Do they actually go out and use their own products 