So far I have only had one rub made on a tree with the tubes on it. I think deer see the larger diameter of the tube and don't recognize there being a tree inside. Of course a wire cage around each tree is even more protection against deer. It's a matter of how much risk you are willing to take. If you have a couple dozen identical trees, the loss of one doesn't matter much.
Its all about the investment to me,if you've watered a young tree,sprayed for bugs/disease etc,weeded fert etc,well if a buck destroyed a tree,you can by another tree,but you cant get the years back .