I have not used one of these before and haven't even thought about them very much. I saw someone shooting one today and was trying to help sight it in, but it would not cooperate. My main question is where does the magnifier go? Between your eye and the red dot, or between the red dot and the target?
Depends on the sight. There are different types of sights. An EO tech holo sight takes the magnifier between you and the sight.
I have always seen the magnifiers setup between the red dot and the shooter. So they go muzzle -> red dot -> magnifier -> shooter.
I have a Romeo 5 red dot on my PC carbine, mounted right over the chamber/ejection port. My Juliet 3 magnifier goes right behind it. The magnifier has a short eye relief (usually not more than a few inches) while the unmagnified red dot has infinite eye relief. So on my PCC it goes: Eye -> Magnifier -> Red Dot.
What might happen if the magnifier were in front of the red dot? With that sort of eye relief would it even work?
Shooter, magnifier, red dot, is the typical order. That's because you are magnifying the image in the red dot, not putting a red dot on the magnified image. The various eye relief issues make having the magnifier in the aft position simpler. The only hiccup is often the length of the rail and how close to the shooter's eye the assembly winds up.
In the intended configuration with the magnifier behind the red dot, the target and the red dot are both magnified in size.The other way around with a long eye relief optic, only the target would be magnified and the field of view through the optic should be smaller. If you have a pistol or scout scope, you could put it in front of the red dot for the heck of it to try it out. Let us know what you think.