The El Salvadoran beach town of El Zonte is visibly poor, with dirt roads and a faulty drainage system. But in one way, it's ahead of the rest of the country: It has Bitcoin.

The tropical surfing spot's basic infrastructure offers a glimpse of the potential pitfalls to popularizing Bitcoin nationally for payments and savings, after Congress last Wednesday adopted the cryptocurrency as legal tender, a world first.

Take Zulma Rivas. The 38-year-old mother of three started accepting Bitcoin payments last year for the bags of cut fruit she sells from a tray to tourists, part of an experiment called Bitcoin Beach aimed at making the town one of the world's first Bitcoin economies.