After too much time spent trolling through DX, I bought this setup and have used it long enough to vouch for it.
The first drop-in from SF died after about two weeks, though, so I imagine there are some QC issues. SF was very good about the replacement. They seem to be very motivated to establish themselves as an "honest" dealer. Shipping was quick from HK--less than two weeks each time.

The current drop-in has been going strong for about two months. I don't have experience with other 18650/tac flashlights to compare it to, but I am impressed with the L2's build quality and brightness. I was running a 2-watt Planet Bike Blaze alone before and this is a whole different ball game. I still use the Blaze for extra "be-seen" light because it gets such good battery life.

Battery life on the L2/XML is decent, maybe better than I expected. I have a 40 minute commute on unlit paths and roads and I usually get 3-4 rides on the high setting (though it appears to vary somewhat by the cell I'm using). I ended up buying SF's charger and four cells, which put the whole package over the $50 mark, but not by much. When the battery dies, though, it dies quickly, and I've had to replace it mid-ride a couple of times. Annoying, but maybe a small price to pay.

It advertises as 820 lumens on high. I can't speak to the accuracy, but I've felt no shortage of light at any speed. I sometimes get flashed by cars, though I've tried to mount it low and angled downwards slightly on my front rack. (I don't feel bad about spilling a little more light than I should--how many times have I been completely blinded by car headlights?). It's mounted with a simple P-clamp. I don't lock it outside a lot, but I never really worry about it getting stolen, despite the city surroundings. It's under the radar enough that I think it's not really noticeable and I don't worry about it too much because of the low price tag.

I considered the MagicShine/clones written up here but didn't care for the complexity of an additional battery pack and wiring. I also like the fact that it isn't bike specific, so that when the next latest and greatest light comes along (or I can afford a dynohub) I can either use the host again with another drop-in or retire it from bike duty and have a great flashlight for home use. All around, a good deal.