In my case flickering was caused by a poorly soldered led.
Both of mine at about 2.1A are doing the same exact flickering, and it's not the switch/tailcap assembly - I can repeat it with a jumper wire. Thinking it's heat related to the driver.
Another way to rule out the tail cap on your light would be to substitute a known good SK-68 tail cap.
Win,win! Also on the Sipik.
Updates:
- easy to take the tailcap apart - apply pressure on the button and it will slide out on the thread end. I got movement with my finger at first, then used the backside of a metal chisel (flat surface) to just apply mild pressure. One problem is the button is too tight up against the rubber. I sanded the plastic button (not the rubber piece) down about 0.07 mm, and seems to work better.Also treated all contacts with DeoxIT Gold. Only issue now is maybe it's too loose. I put in a SANYO unprotected, and the button pushed in when turning it on, so, I added a magnet on the tail of the batteyr and seems to work well now. It's a one piece unit -- the spring is part of the switch, half in, half out. You can open the switch though, prying open very carefully.
- Seemed to solve the flickering I was getting. Removed the resistor on the cap (tried both caps -- no difference), and potted the driver with Fujik grease. Definitely no flicker like it used to. But now I notice when the light comes on in high, the amps is like 1.55A then in 9 secs it changes to 2.05A (expected because strill have the resistor mod). When the light is warmed up, the 9 secs drops to like 1 sec or under, but still noticeable -- weird stuff...
- So my XP-G2 mod'ed light does for lumens: 422 @start, 388 @30 secs, throw: 9 kcd (190m)
- Ohh - did the same thing on my XM-L2 U2 1D version: removed resistor on cap, potted the driver, left on resistor for increasing amps). Light worked briefly in testing, then died - now completely D-E-D. Ouch - no idea, wiring and emitter seem all good... I ordered the 15mm driver from DX (simple 7135 one, here)
:)
Nowthatsfunny ... there is no known good sk-68 tail cap :P
best lube ever made is no-ox-id illumination supply or ebay
Any tailcap that was working two minutes ago on another light is a reasonable option to test with, as well as the suspected bad tailcap swapped to the other light.
Seems like twice a month some new goop shows up. Hard to believe all these miracle in a bottle items have been hiding from me so long.
Fixed my D-E-D problem. Duh me... Poor contact between the driver and the pill/body. can't recall what holds the driver in the pill - think it was just pushed/press fit in, so maybe the potting got in the way. soldered a tab of copper sheet from the edge of the battery side of the driver, and wrapped it over the edge of the pill so it should et squeezed down when the pill screws in. Little hokey, but working well now.
This light http://dx.com/p/mt-104-cree-xp-e-q5-60lm-3-mode-white-zooming-flashlight-golden-1-x-aa-14500-254993#.Uva2fPu7QSl looks like an imitation of it, as one would expect. 
Most lights of this sort, regardless of brand name, look to me like they come off the same production line, but this looks like a legitimate copy. The minimal knurling may be to replace the extrusion with something that suits smaller production volume and tooling cost.
The color is off-putting, but the design is aesthetically a step up imo.
US $2.69 + Shipping Cost
Appears to be the same thing with a one mode driver. Not clear if it takes AAs. Maybe they left out the boost driver. Brand is listed as OEM, which I guess means one can resell it under his own brand.
They also have 3 modes called MK18 for US$ 3.41 + Shipping Cost.
I've been putting mine thru the ringer since buying it from wallbuys for 1.99.
I used an old lumens trick and cut horizontal grooves in the head every 1/4 inch or so with a pipe cutter to give it more grip .Then I filed the groves a little wider with a small set of files to clean up the groves .Filed grooves in the tailcap ..I dedomed it with a razor blade which gave it a lot more throw....then I filed down the bottom of the Head to get the lens closer to the emitter and gained a bunch more flood ..5ft wide beam at 4ft distance .. Lastly i went at it pretty hard with course sandpaper and finished it with a wire brush .Not close to being finished as there is still a hint of gold color .It still needs some resistance mods ..tint is better and overall it's an improvement .I like the fact it deserves no respect and isn't getting any .It looks better in "wire brushed almost silver" than the ugly gold .
Which versions of this have a solid pill, if any? Any way to identify them?
Maybe by how much they weigh?
Says they are “XM-L” now. (sure they are wrong!)
I've been dropping in XM-L2's and XP-G2's on Noctigons -- outstanding little torch. Everyone loves them - did the Fritz the Cat trick with grinding down the zoom slide so it gets a much bigger flood and increases lumens output, as I measured -- just outstanding even with the stock driver. Plan is to build up the OSHPark 15's, but have to check size... So much better than a SK68, in my opinion... I got in a few more, just no time to mod them all. Just ordered 3 more too, from BangGood here, $9.16 for qty 3 after 'blf' coupon.
I cannot recommend banggood version…
Comment links don't work for me anymore - just get a blank page. What's the post # in that thread? I'm interested. Crap - actually I think I got 3 BG ones on order... Oops - it worked 2nd time now... Ok - I see, ohh shoot!!! Maybe I'll get lucky and they will get lost - maybe a refund? 
It's not high qual for sure, but it does sound like BG has an even cheaper version...
A friend just got a UF S5 from FT - cheap 18650 tube light, but man, did they cheapen that light same way - hollow pill, actually totally different cheaper pill than all the other cheap S5's I got... Cheap is going to a whole new level, but the prices aren't any cheaper.
I like these little lights better than the sipik sk68 because they have much fewer sharp edges ,...are much smaller and a lot lighter .With a battery they are 50 grams .VS. a sk68 which is 85 grams w/battery.
Cutting the Head down is simple and makes a big difference ...so does de-doming the xpe..
Overall a good little "must have" budget light
Currrap! Got my 3 silver ones from BG today -- yes chief, they are the same as yours, one mode, hollow pill. The rest look ok so far on the outside - need to look into them further. I tore one apart right away. I could probably get some copper under a Noctigon star - maybe it will be better than the better stock ones then.
Got the BG one too but having trouble removing the pill. Any tips? I’m assuming it just twists off from the front so I took some needle nose pliers and tried to unscrew it. It turned three times and not it won’t budge. How are you getting it out?