I like mine a lot. I am aware of its abilities and limitations and I work around them. It is an overall great scope.
The eye relief is short, and it has been a non-issue for me.
With training it can be used well inside of 50m. It is not as effective as an Aimpoint type optic at 50m and in however. One field expedient way to make it better for CQB is to put the front scope cover over the lens occluding it, while leaving the rear lens open. This makes it into an occluded eye red dot. It works pretty well.
I use the magnified optic except for bad breath distance like 10 yards or closer. Then the iron sights get used. There are many people that use the magnified optic at close ranges too though. It just takes some getting used to, and it reduces the field of view.
I haven't bothered to take off the rear sight, so I can't tell you how difficult it is to do. It looks pretty simple.
The Acog is a great optic. If your job is to kick down doors and the longest shot you wil be taking is 10 yards then I wouldn't recommend it. In most other situations it excels.
Are you thinking of buying one for yourself? What will it be used for? What kind of rifle are you putting it on? What kind of ammo do you shoot?