It is unclear to me: are all M68's CompM2's, or are the newer M68's actually CompM4's?

Also, what are the differences between the M4 and the M4s? The battery housing is positioned differently, is that the only difference? What does the "s" stand for?

from aimpoint's website



"The CompM4 offers a high battery compartment, while
the CompM4s offers a low battery compartment. In all other aspects, the
Aimpoint CompM4 and Aimpoint CompM4s are identical."
Seems the CompM2 is the only one designated as M68

Wikipedia. . .

http://en.wikipedia.org/wiki/Aimpoint_AB

Aimpoint's site designates the M4 as the latest version of the M68 CCO.  When I got out we were using the M3 and the nomenclature was still the same.

i believe  M68 just means aimpoint red dot as far as the designation

M68 SIGHT, REFLEX, W/QUICK RELEASE MOUNT AND SIGHT MOUNT
(COMP M2: NSN 1240-01-411-1265)
(COMP M4: NSN 1 240-01-540-3690)

As shown both the Comp M2 and Comp M4 are considered a M68 CCO.

The M4S is not military issue...........yet.  Only difference is the battery location.

What is the point in making two identical products, except for the battery location? Why would that particular feature be something people would have divergent needs on?

Aimpoints have usually had high mounted battery compartments.  The Aimpoint CS (made for the Swedes) had a low mounted battery compartment (that's where the "S" comes from), and I guess enough folks saw it and wanted a lower compartment.  Theory is that the lower one doesn't infringe upon field of view- not something I notice, but enough for people to care and Aimpoint figured it was worth the investment.

Many say that the M4 is the one to pick if you plan to run a magnifier since the control dial on the M4s is a bit obstructed otherwise, but if you don't have a magnifier the M4s is slightly preferred for the field of view.  I have a regular CompM4 with no magnifier and I don't notice any issues.

Plus 1.
I am issued a M4 but I bought for my own use a M4S.  I do not like the high battery.  FWIW, I do not have any issue with the low control and a 3X sight at the same time.