I don't have either of those others to do a direct comparison, however, I just got my Z-Power light in today and am quite impressed with it. Regulation on it does seem to be pretty good -- I ran a couple of cells in there that were somewhat worn down to begin with, and the light produced absolutely consistent output for quite a while, then quickly dropped output -- this gives feedback as to when it is necessary to change the batteries.
The light I believe is voltage-regulated, (as opposed to current regulated like the Fenix lights) and the multi-levels are accomplished with a two-level switch in the tailcap, one with a 7-Ohm resistor. I would say that at close range, high (a bit over 4W total, including driver and resistor losses) and low (about 2W) look only slightly different, however, for long range the high mode is noticeably brighter -- I would say run it on low (half the total power consumption) most of the time, and only switch to high as needed.
One drawback that I did not like is the interface on the tailcap -- the stock one is off -> low -> off -> high -> off. This means you have to turn the light on then off again to switch brightness, and the next time it comes back, it is the level that you didn't find useful before. My "fix" was pretty simple in that I had a Vinet onhand that I bought from Dealextreme earlier -- I simply swapped the tailcaps. The Vinet tailcap is off -> high -> low -> off, also with a 7 ohm resistor. (I'm considering swapping in a higher resistance so that the "dim" mode is somewhat dimmer -- the low on this is actually still very bright.)
Build quality seems to be quite nice, the light feels fairly durable. Also, heatsinking is quite effective, when running the light on high, the entire body heats up consistently.
