The reason why we're creating it is to stop one person from getting super rich on the backs of whole world.
For example, Uber.
They won't be able to become so wealthy (even though their price is pumped up more than value). They could operate everywhere, but they will be paid in local currencies without having an option to exchange so much different currencies into $.
Let's say they operate in 100 towns. They would earn 100 different currencies which they won't be able to use for anything outside of those towns.
Why would someone in Silicon Valley become rich because every taxi driver has to pay them 25%?
That's called mafia style.
This way, drivers will be able to keep 100% (like they were before), locals have more money, more job opportunities since it boosts local production etc.
Bristol did that, so it proves that it can work.

Cuba's problem isn't local/international currency. It is US embargo.
Take a look Venezuela. Their currency has super low value. Average salary is like 3-5$...Why? Because US want's to put their guy on the top of their country...so they destroy the value of local currency, prevent them from exporting local goods etc.