This will work on vinyl gutters.
The USeal Band 6 in. Aluminum Foil Self-Adhesive Repair Tape has a heavy aluminum facing with an extra-thick rubberized asphalt-based adhesive system. The aluminum facing is embossed to provide flexibility for wrapping irregular shapes and surfaces.
It would hold together when used over a dime sized hole or a 1/4" crack. It's stronger than duct tape, but it's not a solid patch material. Example: If you have a dime sized hole in the bottom of the rain gutter on your house, this works well. If you have a basketball sized hole in the floor pan of your car, not going to do the job.
This holds up well in full sun and on a metal roof
No, it is one sided, I used it on my shed roof, and no more leaks, I love it
While it could be great for closing up an air leak, it probably has almost no R value. Keeping cold air in the winter from blowing into your heated space is a good thing, with or without an R value.
No, this is not flammable.
If I'm not mistaken, my maintenance guys do not use a primer to apply this. It sticks and does extremely well.