It's practical as long as you're using modern equipment. I buy US games on Steam using Canadian dollars and it does the purchase according to the exchange rate at the time of purchase.
It fails when doing simple transactions. My barber takes cash only, no credit or debit. Must use a certain type of currency. No Alabama bucks.
So you're comparing a multi-national company (Vivendi) to about 2/3 of the transactions in this country, which are local small businesses?
It isn't practical, at all, even on the multi-national company level considering the complexity is not linear, it is geometrical. Considering this volatility directly translates into earnings impacts, whether through hedging or currency shifts, it would eat into the bottom line of even the largest and most sophisticated companies. For smaller companies they would take huge amounts of currency risk since they are very unsophisticated at that level and wouldn't have the economies of scale needed to appropriately hedge the risks.
Then you consider the fact that the vast majority of transactions take place on a credit card and, if the vendor does not want to take currency risk, they will merely demand you pay in currency X. This means that if your currency is one they accept you will have to convert it at your bank level. This also means that your bank will not take the bid/ask spread risk associated with your transaction, which will cause them to balloon out the bid/ask spreads to hedge their own risks.
So then you have your costs skyrocketing to deal with that.
Eventually the inefficiencies would result in a single currency anyway.
However, explaining practical things, like currency risk, to a libertopian is akin to explaining calculus to an infant. They simply do not have the intellectual capacity nor simple logic to understand that their viewpoints on the world are infantile and naive.
God help us if they ever get enough brain-dead idiots to follow them.