This is an interesting comment. It was 3 stars and he had a price issue at 30 dollars each so his house could cost 150 dollars.
Yes, that may seem like a lot of money. But look at the alternatives.
A roofer will charge around 300 dollars at least to do 5 vents, pull shingles, and maybe leave a less than desirable looking repair. Also you have to go through the hassle of scheduling and waiting for him. These repair the vents easily with no special training, no shingle pulls, and its done at your convenience. So Critter Quitters are a bargain.
How about some wire mesh, foam, and a hose clamp. You can do that if you wish. It will last a while. But its time consuming, ugly, and the foam you squirt into the damaged portion of the vents not going to last forever. Critter Quitters will last the life of the house, so when you re-roof there is no need to take them off and replace your vents. (much to the dislike of the roofer)
How about not doing anything? That’s a gamble. Chewed vents are roof leaks, and if you have a lot of rain that’s going to cause damage. In addition, the squirrels aren’t going to stop and may gnaw it down to the roof line in which case you have a water fall into your attic everytime it rains.
So when you look at the advantages, the cost is really inexpensive.
Here is the comment.

This is too expensive to put on all the vent pipes on my house, which amounts to 5. $150 to foil the gnawing squirrels. Sheesh.