Something like that going on here as well, I bought one from DX and one from Kai about a month or so back. The one from DX came last week, the one from Kai this week.
The difference between the two is so big I wonder if they were even made in the same factory. The only thing that seems to be the same on both lights is the black switchcaps.
Some differences:
-The DX one has a Cree with a silver base, the led on the Kai has a yellow base.
-The DX one has a screw in reflector and the Kai one just sits loose
-DX, O-ring at lens...Kai, none
-They use different swithes, the DX one seems more solid. Swith assembly is different too, the DX one has a more solid construction.
-The pill containing the LED and driver looks different. Better finish on the DX there.
-The writting on the head is a different style on both lights.
-The DX one is a lot brighter, and has a much smoother beam. Much more rings in the Kai's beem.
-DX, orange o-rings, Kai, black
-The grooves on the tailcap are bigger and further apart on the Kai light compared to the DX light.
And most clearly of all, the finish:
The DX C3 has a smooth brushed finish, the threads are a bit rough, but other then that it's a nicely finished light...
The Kai one on the other hand, well, they only machined out the parts, but there seems little finishing done after that. It still has the machining grooves all over the body and the tailcap, only the head seems to be smoothed somewhat. It also has sharp edges all over the light.
The both share the gaps though, but I put some thin black o-rings in those, and that gives it a pretty nice look. Nicer then the gaps anyway, if you ask me
Ofcourse, I can't say if this counts for all the Kai and DX C3's, but to me the DX light is the clear winner, it actually feels like a light that's twice as expensive as the Kai C3.