What are Key-leveling Tabs made of?

Except for the eyelets, they are made almost entirely out of paper.

How long do they last?

They are made out of materials that should last as long as, if not longer than, standard paper punchings. Prolonged, direct exposure to UV light may reduce life span.

What keeps the tabs from sliding or canting?

There is a layer of premium, non clogging, 400 grit sandpaper on the bottom. The weight of the key on top prevents it from moving- even if the key is chucking. They do not pivot, and won’t interfere with their neighbor tabs as long as you pull them parallel to the key buttons. You can test the friction principle by putting a strip of sandpaper, grit side down on a piece of bare wood, and trying to move it by pressing on the back with your finger or a balance cloth punching. It won't move in any direction since there is far greater friction on the bottom, which is increased, the more weight there is on top.

Do they make noise?

No. The only reason they might make noise is if they are not properly installed.

On a grand piano, will they ever catch when I pull the action in and out of the piano?

No. They are somewhat stiff, and under the weight of the keys they do not hang much, even when fully extended.

Do Key-leveling Tabs affect Down Weight?

Yes. They reduce down weight by approx. 1 gram.

How much time can I save by using Key-leveling Tabs over conventional paper punchings?

Depending on the quality of the piano, on a precision leveling, you can save from 2-5 hours initially, and once in the piano, every leveling job thereafter, full or partial, has significant savings of time and effort.