Bought my share of them. Chance of a jackpot was tempting. Used some on mail to overseas collectors. Overpaid the letters, but I think they enjoyed them.
Found three unused sheets in a stock book the other day (opened).
Anyone keep some unopened. (Like Schrödinger's cat), until you open, there could be a chance.

To the sudden increase in numbers. hopefully the coil roll scammers have not entered the game.
pat