Using Atomic labeling scheme, a B2 would infer that the 2nd stage is Brass. Up to now all of the 2nd stages are titanium except for the Z model. I have 2 identical atomics which are brass 1st stages and Titanium 2nd stages. One has a front cover on the 2nd stage printed B1 (brass 1st, which it is) and the other one has T2 printed on it--these rigs are identical. I can think of no reason for Atomic to make a brass 2nd version unless it surplants the Z. If I could afford it, I get the M1, if only to get the wider exhaust tee. The fact that it does higher % of O2 can't be a bad thing. I bought my 2 atomics off a dive buddy for $250 apiece (he paid for having them serviced). They were about 18 months old. Atomics are rated #1 in nearly every comparison test done including DIVERNET tests. If I knew nothing at all about regulators but was forced to buy one, it would be from the short list of SP S600, Atomic, Aqualung Legend LX, or Apex. If I have the oportunity to tryout many different regs I may find something better for me (I like my Cyclons, and they never come out good in tests...). The lightweight 2nd stage of the Atomic is nice, but most 2nd stage fatigue really comes from fighting the hose more so than the weight of the reg. The only thing you won't like about the Atomic is the grease packed into the 1st stage since it oozes out ocassionally.
Cheerio,
Mark
