This review was for for an installation done on Feb 27. 5 stars.
To address the comment about the vent height, the units need to be tall enough to fit most common flashings, which are 9 inches when folded over the vent pipe. Its not necessary to cut them down unless you wish to, they are designed to drop rain into the center of the vent as long as they are centered over the top. Also a saw is the best way to cut them, tin snips are better for trimming them for tile roofs.
While a little expensive, I’m glad I purchased 5 of them for my roof. Squirrels had done a number on a couple of my lead wrapped vent pipes, and were sure to move on to the next. These stopped them in their tracks. I no longer hear them in that area, and no sign of them in a couple of weeks! In Florida, we have shorter vent stacks, sine we don’t get snow. I cut off a few inches of the Tough plastic so the upper water drip tube was fully inserted into the top of the vent pipe. They were far too tall. It looks better too. Good luck using snips on this plastic! Use a power saw!