I do not have CR123A lights, but will try to describe the difference between my Fenix and Ultrafire AA/AAA lights.
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Fenix L1T v2.0 vs Ultrafire C3 Q5 (1AA):
Fenix L1T
Tighten bezel for turbo, loosen bezel for low. Click for on off.
(With the L1D/L2D/P2D soft press in turbo brings you strobe; soft press in low brings you to medium then high then SOS. If you are in off mode for more than 3 seconds you always start up in turbo or low depending on bezel position. You never see strobe or SOS unless you want to.)
Ultrafire C3 Q5
5 mode with memory - medium, low, high, strobe, SOS. Soft press to change modes; wait x seconds to come back in last mode. Say you are in medium, soft press or 2 will get you to low or high. Now you have to cycle through strobe and SOS to get back to medium.
Fenix has some of the most efficient boost circuits so runtime is longer at the same brightness level with the same battery.
The trade off is you cannot use 3.6V RCR123 Li-ons (14450 for my L1T (also L1D)) in a Fenix. The cost of primary CR123A is a concern especially if you need one in a hurry.
The Q5 in the Ultrafire is slightly brighter (maybe just whiter) than my L1T RB80, no big deal in normal use. The allowed use of a 3.6V 14500 vs 1.2V NiMH lets the Ultrafire run way brighter. (This will be less when comparing a 3.0V CR123A with a 3.6V RCR123A.)
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Fenix L0P SE/L0D CE vs Ultrafire 602c (1AAA)
The Ultrafire is a clone of the single mode Fenix L0P and mine works as advertised. But 1/2 my batteries won't fit.
The Ultrafire I got is rated for 3.6V 10440 (note other models do not). It limits the current to 450 mA. The 1-1/2X brightness is not noticeable in real use.
The Fenix are not rated for 10440 and doing so will void the warranty. However it will run at 1200 mA and be awful bright. The battery, LED, and circuit board are all running way beyond design limits and there are reports of failures.
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Fenix has fairly consistent QC. The Ultrafires, MTEs etc from DX have very spotty QC. All 5 of my Fenix multimodes go back to default after 3 seconds. The DX lights vary from less than 1 second to more than 10 seconds for memory to kick in. That is why I said x seconds earlier. This is not a problem with 1 torch but with multiple torches remembering what timing goes with which torch can be a problem.
If you are in the US 4sevens provide excellent service. Replacements for faulty units are sent right away.
Try do a return to Hong Kong/China. The postage alone is 1/2 the price of a new light. And the wait for the faulty light to cross the Pacific and the replacement to come back the other way.... When combined with the lack of QC in the DX lights.....
I have bought from DX/KD
1 No name AAA - died in 1 week;
1 Kai 130 lumen 3xAAA - there is an electrical leak, my batteries drain down when not in use, light cuts out when I tilt the torch;
1 Ultrafire 602c AAA/10440 - some batteries won't fit, otherwise working;
1 MTE 5 mode SSC-P7 - really fast timing <1 sec for memory (I was stuck in strobe not knowing how to get out the 1st week), others reported <10 sec, otherwise working;
1 Ultrafire C3 Q5 AA/14500 - another CPF member broke his switch, I sent him mine and it broke within a week, the head still works on my Fenix/Civictor V1 body;
4 MTE single stage AA - all working;
1 Romisen RC-W4 3xAAA - working.
Note only 1 light does not work, a lot of them just does not work too good.
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All my Fenix lights except my original L1P are working.