I’m not sure if you count the penny (or any other US coin) as “successful” or not, but that peg has not led to calamitous money outcomes for the US currency system.
It’s also due to the difference not being worth the effort most of the time but that doesn’t change the refutation of the claim that no pegs work. The penny peg works even in a world where the actual utility of a 1/100th usd coin is probably negative.
§ 82.1 Prohibitions. Except as specifically authorized by the Secretary of the Treasury (or designee) or as otherwise provided in this part, no person shall export, melt, or treat: (a) Any 5-cent coin of the United States; or (b) Any one-cent coin of the United States.
https://www.law.cornell.edu/cfr/text/31/82.1.
Click "next" on that link for the special exceptions, which do allow for modifying small amounts of these for jewelry or decoration.
This is actually exactly analogous; many people don't realize that the status quo of "multiple denominations" have ancestral ties to bimetallic currencies of the sort covered in this article.
It would have been difficult for Henry III to de facto outlaw smelting of gold coins because the scale of the gold penny's distribution was much smaller (making attribution of a smelting operation much harder), and because the ability to surveil this sort of activity was severely limited by geography.
But melting down US pennies is de jure illegal (nb: only since 2007 [1]) and the number of pennies you'd need to smelt down in order to justify the effort would probably make the sourcing operation noticeable to authorities.
[1] https://www.usmint.gov/news/press-releases/20061214-united-s...