> Fortunately, complementary currencies are now legal in just about every country, as evidenced by the popularity of cryptocurrencies, one form of a complementary currency.

In many countries, cryptocurrency is considered a commodity - not money - and therefore disposals (where a cryptocurrency is given up in exchange for something else) are taxable events.

This is quite inconvenient and complex compared to money, and only less so if you are fortunate enough to be using a cryptocurrency that is pegged to your local currency (eg USDC or mUSD in place of USD).

Furthermore, if I understand it correctly, the purpose of complementary currencies is to act as a form of capital outflow restriction: you have a limited amount of capital in your town, and you want it to remain in your town alone. A complementary currency, which can only be spent locally, restricts the outflows of capital and allows it to remain local and do useful work multiple times within your town rather than potentially enriching other towns.

Cryptocurrency doesn’t intrinsically do that at all, although there are certainly some tokens designs that can replicate it eg LP emissions on decentralized exchanges.