Ok, went to look at specs. The operating range of the M31 219B is .8v-3.3v(1.8v needed for full output) So this would be the same module used in the AA MDC that is oos and may/maynot become available again. So an option for someone that wants the nichia AA MDC could buy the MDC 123 w/nichia that is still in stock and also buy the MDC AA body and have both options.
on a side note: Here are my wonder twins for the day. I say this because they are not stock, both have hi/lo with M361 N(219B) for 6 levels on ea light.
Bravo has M361 219B, I rebored the oveready bored body to accept any size protected cell (stock only accepts AW protected cells that I am aware of) Also if you pay attention, I enlarged the output side on the bezel as large as possible (this dramatically increases the spill area without effecting any stock performance) To give you an example: shining at my garage wall at a throw distance of 18' the stock beam diameter is approx 18', enlarged at same throw distance of 18', the beam diameter is now 24' (that's a huge difference when going out into the real world!)
Likewise, I have an M361N in an MDX 22.3 head compared to the normal 16.5 head. I get similar results (I now get the same 24' beam diameter at a throw distance of 18'. My stock MDC 16650 500lm Neutral has a beam diameter of approx 26' at the same 18' throw distance.
Anyway, just thought I'd share my experience and accomplishment