I do a lot of volunteer work at some wildlife refuges near my home. We have planted about 20,000 trees and shrubs and have used tubes on many of them with mixed results. Here is my advice:
1. First, you should have a good idea what you are trying to protect your trees from. e.g. voles, rabbits, deer, beavers, cold weather,

These will determine what type of tube to use, and how you place the tube, or even if you should use a tube at all.
2. Tubes work well with trees, not so well with shrubs. I can explain if you'd like.
3. Your summer weather is important. e.g. we have had some trees die in tubes because they got cooked in the summer.
4. Slow growing trees will probably need to have their tube stakes replaced at least once. Otherwise the stakes rot, the tube falls over, and you end up with a tree growing at an angle.
5. Deer can kill plants in 2 ways: 1) by browsing them to death; and 2) by bucks rubbing their antlers on young trees, rubbing all the bark off.
Overall the main reason we have had plants die is due to competition from non-native grasses, e.g. reed canarygrass. The non-native grasses suck up all the water. We have also lost a lot of plants due to weed whackers - they were trying to cut the grass back to give the plant a chance, but inadvertently cut down the plant. So if you have tall grass, flag your plants.
In my yard at home I have experimented with using bamboo branches as a rabbit deterrent and it has worked surprisingly well. The idea is to place bamboo branches in the ground around the plant, forming a tangle of sticks which the rabbits usually avoid. The nice thing about this approach is I can place the plant and the bamboo branches, and I never have to come back and remove the tube. By the time the bamboo branches rot, the plant is usually big enough to survive the browsers. However if there is nothing else tasty around, a determined rabbit could force its way through the sticks.