Presently, there is no alternative allowed to be used as currency.
This is either an outright lie or misinformation.
You can use anything you want as currency, it's called barter, and has never been illegal.
What was the part that got Liberty Dollars is the obvious confusion over claims of it being US backed and currency, ie, legal tender.
Seriously, they should just write in huge letters on the back, "THIS IS NOT LEGAL TENDER ACCORDING TO NORFED AS WELL AS THE US GOVERNMENT"