Lambda,
I'm a light collector other than flashaholic. I have a number of pocket lights and penlights fitted with the Tektite L222.
The L222 uses a 5 MM LED that is badly overdriven, but at the same time is very well heatsink'd.
The L222 kills the LED for any input voltage above 3.2 Volt, and is too sensitive to any variation of the LED Vf.
The boost converter of the Tektite L222 uses a blocked oscillator that is prone to feed the LED with more current than necessary. It stops working at 0.8 Volt when there is no more bias. (to date the only converter biased from the output is the one in the Arc AAA, that works with 0.4 Vin).
I ended up using zinc-carbon cells in my Tektite L222 upgraded lights, to avoid some alkaline batteries (that have 1.68 V open circuit) to fry the expensive drop-in.
A MJLED replacement for L222 would be welcome and, very likely, less expensive, more reliable, and brighter...
Anthony