What are the benefits of a common currency? It allows easy price comparison between goods and services in different countries and permits a company in one country to easily purchase goods and services in another country.
But, if I have a credit card and a smartphone, I can be in Colombia and purchase goods at a known price in my home currency about as easily as I can anywhere in the € zone. The problem I have is with any trade barriers between the countries, but this means the trade barriers are creating the, well, barrier to trade and not the currency issue.
Meanwhile, the currency movements which were erased by the adoption of the € mean that countries have to address their relative ability to compete by making harder poltical decisions to cut wages rather than just letting the currency depreciate and make everyone less wealthy.