IMO, lumping tech and DIR together is a mistake.
An example of that is in the section discussing that the "may choose not to have a console". A DIR diver would never choose a console.
And this section
Secondary regulators can be of the piston or diaphragm type and can offer adjustment knobs to adjust the cracking pressure (the pressure differential at which the diaphragm to piston opens to allow breathing.
Doesn't make a whole lot of sense to me. The first stage is piston or diaphragm no?
*shrug*
To me the discussion should contain information on:
First stages: Diaphram or Piston, DIN or Yoke, Seal or unsealed, balanced or unbalanced.
Second stages: Primary and secondary, balance or unbalanced
With explanations on each additionally with info about servicing intervals, local service, and considerations while traveling.
Finally, your examples where you suggest using an unbalanced reg to for extreme diving, I don't see where that comes from. And why a side exhaust? All the doubles divers I've gone with have used Apex, Scubapro or Atomic, not a side exhaust in the bunch.
Just my 0.02
