Crap.
I can pretty much sum it up with that one word. An XM-L U2 should be driven fairly hard to maximize its potential but this thing is only drawing ~1.6A on a freshly charged XTAR 2600. In comparison, the 3-mode UF XM-L T6 drop-in is drawing ~3.1A from the same cells. You can easily tell the T6 drop-in is significantly brighter. I'll probably use it for parts. I'm glad I purchased it for about $10 before the website makeover. They have it listed for $16.47 now. So NOT worth it.
Thanks for warning us!
Ouch. Just ordered it some days ago (for modding my 3xAA mini mag).
Let's hope I'll get a better one.. I'll confirm later how bad it is.
Some P60s have drivers which draw about 1.5A on a single 18650. The Dereelight 3SM XM-L is such a pill. Drive it with 2 cells.
Your KD one is listed to do till 18V.
Yeah, I figured the 18V rating meant it would perform poorly on one cell. I wasn't certain of this, but maybe I'll cut them a break in case this is indeed the reason for the low draw. I was searching for a 3.7-4.2V single mode but they didn't have anything in that voltage range. I was actually gonna go with the 5-mode since it's been confirmed but then I came across the single, which is really what I wanted for a forward clicky light. It can't be better regulated to where it draws ~2.8A on one cell and less with multiple cells?
EDIT: Screw that! 
How many P60 lights run off of multiple 3.7V cells? It shouldn't be that common to where an XM-L drop-in totally under drives on one cell.
Really don't know, you need to check that out with 2 cells, a DMM and a light meter.
Actually I am already done with P60, extremely low efficiency. The current draw tells nothing at all. I got the Dereelight because that is 3C and very good quality (pretty much better than Solarforce) and somewhat good value. (check out my thread).
With 2 cells you can be fully current regulated. Though with the cells that are accessible to us, the capacity takes a bit of a hit. (luckily we have the generic 18350 IMRs from BIO)
It's a bright light, no reason to avoid it. It doesn't draw any more amps with 2 cells, it draws less. Half of what it draws from 1 cell. When volts doubles, amps halves, right? I have state-of-the-art multi-fuction measuring device called Eyball mark I, and according to that the mentioned dropin run on two cells is about as bright as MF 3-mode XML on one cell. But it keeps going for ages on one charge, unlike MF 3 mode.
I got one sent to me by mistake. Took a quick look at it last night. I can’t remember the exact number but I only got around 500 lumens. It looks bright enough but the light meter was unimpressed.