Just received mine at work. I bought an M30 for it and am currently running it on a BS CR123. The plan is to run this with Battery Station's 900mah RCR123 cells. I will compare runtime vs. AW 750mah RCR123 when I can. The BS rechargeables are new to me, so I don't know what to expect.
Anyway, the light is well made and small. The head is relatively large for the reflector diameter, but since it's an optic, based on a SF drop-in, I knew it would be. As mentioned, it has very smooth threads. It will continue to screw in for an additional 720 degrees after the light comes on, but it doesn't need to in order to properly operate. When unscrewed enough to turn the light off, the battery rattles around a bit.
Since I intend to keep this light around the office in case I need to inspect or work on something, I bought the flat tailcap model. The lanyard model would be more useful for carrying. Well, that's the good, bad and ugly so far. Oh yeah, it's plenty bright -- even with primaries.