I haven't seen a ton of info on these lights, and I've heard mixed reviews about Nanight, anybody want to add any topical experience about them?
I have a Nanight C3 that I've used as my everyday light, cold water diving, both day and night. I've had it for the past 3-4 years.
It's powerful enough, the battery lasts through multiple dives (a few hours burn time on default setting of 3/4, about 1-2klm by my eye). The head is quite large, but it's not any problem in practice.
It has a narrow spot (5°), but I have one buddy that was complaining about the wide spill and how it might not be a perfect light in a cave. Works well enough for signalling in murky open water.
I have both the Nanight carbon fiber handle and the aluminum handle and the aluminum one is better, the carbon one digs into the hand and is quite uncomfortable. Even the aluminum handle is not ideal, the size adjustment is quite clunky compared to, say, Halcyon Goodman handle.
Overall quite happy with it, I'm not considering upgrading at this point. I got mine for slightly under 400eur second hand.
The canister developed a problem at some point where the charging port was leaking current when disconnected, which lead to slow corrosion in fresh water and then corroded rapidly during a short trip to Mediterranean; I bought a replacement charging port from Nanight, got an upgraded charging electronics for free included in the package and a manual on how to replace parts within the canister. It's been without any problems since then. Overall happy with the customer service and support.