Has anyone ever used stick floor tiles for a counter top?

I would not as bacteria can get into the cracks and mold can grow there.

No, but I used it as a backsplash, and it would pop loose in some places when I put it over other stick tile. So it will probably do the same if you don't sand the surface. (I tried to take first off and change color, but it was destroying the wall.) I could also tell where the one butted up against the other even on the first. On cabinet top I would think dirt would work in between tiles. If you caulk it, then you have grout to clean unless you can seal it. I hope it works out for you.

While clever thinking, they will not hold up or stay stuck on a surface that sees constant, hard wear such as a countertop.

Hi Deborah, I don't know how well the old vinyl peel and stick floor tiles would work on a countertop, but I have seen DIYs online where people have used the newer peel and stick tiles for that purpose. https://www.hunker.com/13402829/how-to-use-peel-stick-tiles-on-countertops

Agree with Marylou. It will be impossible keep the counter top sanitized to the degree which is required in a kitchen.

When the tiles start peeling off, you will have a big problem trying to get everything off without further damaging the old countertop underneath.