I am answering my own post for the benefit of future searchers... I have received these lights and played with them in a bucket of water, but they haven't gone diving yet.
Externally the
Photic 1000 XM-L lights are exactly like the
Photic 900 MC-E versions except for the label. The tail cap and rotary switch also feel the same. (You really need to add some grease to the o-rings, otherwise the tail cap is a pain to turn.)
The XM-L emitter is clearly different looking than the MC-E, and according to my instruments, this light is indeed a little brighter as the specs promise. The constant-current driver does a fair job of keeping the light at a steady output level throughout the run time. It isn't perfect, but the slight drop in output power that I saw with instruments wasn't noticeable to the eye.
With the blue batteries provided, I got 1 hour of run time at full power. (The product page specifies 90 minutes.) With red Trustfire 3000 mAh cells, I got about 1 hour 50 minutes run time. I only did one run-time test of each battery type, and YMMV.
After the light cut off, if you left it on it would turn on and off a few times over the next few minutes. If you turned the power down, you could eke out a 5-10 more minutes of juice after the high power setting cut out, but it wasn't very reliable. Compare this to a non-constant-current driver, where the light slowly gets dimmer and dimmer, but you get
some light reliably for much longer. Which is better? Depends on the user.
After running the cells down a few times I saw no drop in output power, or evidence of discoloration in the LED emitter. That is something that DID happen to me with the MC-E version of the light--it cooked itself after just a couple of uses! Looks like the XM-L emitter in this light is not so afflicted, and this seems like a good product if you are interested in a bright light on a budget and don't need extreme run times.
I will know more after heavy use on an upcoming dive trip, where I'll be putting 2-3 sets of batteries through the light every day for a week.
