Ok the simple answer is this:
TA31RCO-M4 - Bullet Drop Compensator Calibrated for a 14.5" barrel, firing a 62 grain bullet, inludes horizontal lines in reticle, inludes knob cover tether
TA31RCO-A4 - Bullet Drop Compensator Calibrated for a 20"" barrel, firing a 62 grain bullet, includes horizontal lines in reticle, includes knob cover tether
TA31F - Bullet Drop Compensator Calibrated as an average between 14.5" and 20" barrel, firing a 62 grain bullet, does not include horizontal lines in retical, no knob cover tether
The Horizontal lines in the sight picture are in place so USMC team leaders can reference and direct targets to the team, ie target is 3 and one half spaces left of the vehicle behind that brick wall.
The difference in accuracy, in this case "elevation of point of impact" is negligable up to 300 yards. Beyond 300 yards it is variable based on choice of ammunition, barrel twist, barrel length etc. But as a general rule if you were to place say the TA31F on an AR with a 20" barrel it would be approximately 1 MOA off in elevation, or 5 inches at 500 Yards.
If accuracy matters to you at varying distances than my advice would be to match the ACOG to the weapon. If you are never going shoot beyond the 300 yard line than you should be able to use the less expensive choice without really sacrificing accuracy.
Hope this clears things up for you