I will agree with one thing! It is hard to shoot tight groups with the red dot because of the amount of target it covers. I buy the smallest dots I can. I find them much faster to aquire then crosshairs in a scope and you don't have to have your eye right in line, as long as the dot is on the deer it will hit. I use them on all of my revolvers and they are the best for deer. It depends on what is important to you, paper targets or deer. I would put one on a crossbow, but not a compound because it has to be adjusted for every range unless you know exactly how much to hold over or under.
I do use a scope on my Ruger Mark II for squirrels because I have to shoot tighter for head shots. Trouble is that every quiver is magnified and it is hard to hold still.
I also agree with the other poster that a crossbow can break cheap scopes.