Company scrip is a problem because the tokens are usually artificially priced by the issuer above their market value. If Walmart tokens in Mexico were traded freely, they would have had non-zero value (the ability to buy something at Walmart is better than nothing), but less than their face value. The same thing happened with government money many times, so there's nothing new here.

Having a law to always accept some currency in some jurisdiction is convenient, but non-essential (given the availability of exchanges and overall liquidity).

At least in the United States, a vendor isn't required to accept U.S. dollars for sales. Only to settle debts. If you have a shop, you are free to only sell your wares for loonies. If you're a restaurant, however, and collect payment after the meal, i.e. after issuing credit, then you must accept legal tender.

That's really interesting and makes sense. However, given how common credit is, the fact that you must accept USD as payment in the US means that USD circulation is going to be really high, and therefore vendors that don't accept it for sales are going to be demolished by others that do. As opposed to BTC, where if you don't accept it, so what? and if you do, you're at least a little unusual.