There will come a time when your cat needs to be muzzled so that you can cut its nails or other aspects of cat care.
Cutting our cats nails used to be a dangerous endeavor. With the muzzle on we didn't have to worry about her teeth getting us, just the claws. She was still a handful but without the muzzle we would be paying big bucks for the vet to do the trimming several times a year. Then we got the Cat Sack. We can just have the paw being worked on out and the others are in the nylon bag where they can't hurt us. She looks pitiful with her little executioners mask and flopping around in her kitty straight jacket but it works.
As for the size of the nose opening for breathing, we have no worries about that. The fabric itself is breathable, the opening isn't all that small, the muzzle doesn't fit that tightly so air can get in around the perimeter and it is only on the cat for a few minutes.
This is the best purchase I have made recently!! I have been fighting with my kitty for 14 years when it comes to nail trimming. I put the muzzle on and kitty just completely relaxed. I was able to trim all nails on all four paws with no stress to kitty or myself!!