What he may have been talking about, and I agree with him on, is the amount of "wiggle room" you have behind the optic.
The T1/H1/R1 series has a smaller viewing area in which the dot is visible which, if you run it way out towards the front on of the gun, means you have to have a more "precise" cheek weld to see the dot.
The M4/M4S has more area to see the dot, which means you have more room to have an imperfect cheek weld. Especially if you run it towards the front of the gun.
It is very noticeable to me.
One of the reasons I actually prefer the M4s, even if it is heavier than the T1 series.
However, they are perfectly suited to using on a rifle, just not as forgiving of poor cheek weld that the larger optics are.
I am no longer participating in gun forums.