I prefer the Nuwai Q3.
My opinion says:
Nuwai has better beam quality. Balance of flood to spot, no artifacts in beam. Longbow is spot beam mainly with noticable artifacts.
Exterior fit and finish are about the same, with an edge to Longbow due to tougher finish options (HA 3 in the olive drab model). I'd classify exterior fit and finish to be very good on both lights. Interior fit and finish on both lights are below average though, unfortunately.
Runtime: I get 20-30 minutes of regulated runtime in my least efficient Longbow Micra (I find this runtime annoying, and it happens to also be in my c.u. green tinted Micra), and ABOUT 45 minutes minutes regulatated runtime in my most efficient Micras. My Nuwai Q3s average about 1 hour to 75 minutes of good but diminishing light, then poop out and give minimal light for a few more minutes, depending on battery. This is a slight advantage to Nuwai, as there is less variation and about 10-15 minutes longer runtime on average. Both lights from what I can tell clearly do NOT live up to the runtime they put on the packaging.
Tint: My Nuwais are both HID blue, which I don't mind. Only a slight hint of blue when looked at in some directions. My Longbows range from nasty c.u. green to creamy near white. But, even the ones with the white beam have some hints of green in the corona due to the optics making minor but strange colored rings. I've fixed this on one of my Micras by dropping in a reflector. I'll give an edge to Nuwai in tint, since I really dislike green tint (especially the c.u. green tint).
Output: impossible for me to measure lumens since I do NOT have an integrated sphere, but my eyes tell me that the Q3s are apparently giving more OVERALL light (lights up a larger area much brighter), but doesn't throw quiet as far as the Longbow Micras.
Overall, both are good products. I think the Nuwai gives more bang for the buck, and for me the excellent Nuwai beam quality is enough to overlook that it is unregulated and lacks HA 3. I definitely prefer the Nuwai, but still use both Nuwais and Longbows.