The brands that you mention, Halcyon, Dive Rite, and Salvo will all serve you well. I have or dive with people that have all 3 (I can’t speak about the others since I have no experience with them) and if taken care of, they will take care of you.
As far as I’m concerned 10 watts IS enough. Sure I’d like 21, but it isn’t enough brighter to justify the expense while my 10 watt keep burning. There’s no real difference in the light output of the 18 and 21 watt, it’s just a different mfg, so your choice is really 10 or 18/21.
Make sure you get one that is focusable. A non-focusable 10 watt may leave you wanting a little more.
You’ll probably want something with at least a 4 hour burn time, but depending on the diving that you’re doing you may want considerably more…or at least the ability to have a second battery to slide in. As mentioned before, Salvo’s new design has the battery integrated into the canister. This is a nice design, but you can’t change out the battery unless you have an entire separate canister. If you go this route, get a bigger battery than you think you will need. Also, depending the type of battery; NiMH, LiIon, LiPO, etc…there may be different ways to handle it…keep it fully charged, store it drained and charge before using, etc…see what the mfg has to say about it and follow it.
Lastly, the primary light is a GREAT tool, probably some of the best money that I’ve ever spent. It has the ability to change the way that you dive and communicate underwater. Spend the money and get what you want…you won’t be disappointed.
Enjoy!
