This is incorrect. Things are legal unless criminalized, and tumblers are not inherently illegal, and have plentiful legitimate uses. However, money laundering

This is incorrect. Things are legal unless criminalized, and tumblers are not inherently illegal, and have plentiful legitimate uses. However, money laundering or offering a money laundering service is illegal and so using one in an effort to money launder, or facilitate such, would be illegal. It's akin to something like a jimmy bar. Owning or manufacturing/selling them is 100% legal, but they're going to be used pretty regularly for illegal purposes which is, rather tautologically, illegal. Similarly, intentionally selling them for illegal purposes would be illegal.