I will respectfully argue the opposite: screen them. I lost several trees over the winter that had been in the ground for three years due to mice making nests in the tubes and girdling them. It was painful. However, I started using aluminum window screen to wrap the trunk two years ago and didn't lose a single one of those trees, out of hundreds. Better safe than sorry. It's also important to clean the tubes out at least once a year. I general do this when I spray around them for weeds in late May. For volume and short term ease of installation, tubes rock, but in the long term, caging is less work.
Also, window screen stapled to the terminal leader also keeps deer off of your conifers and prevents your losing a year's growth to deer with the munchies, but remember to take the screen off in the spring to let them shoot up.