I do remember that the anime adaptation (Mermaid Melody: Pichi Pichi Pitch) made it into my country, and was broadcasted on TV like 8 or 9 years ago, and it was quite popular between girls at the time. I didn't payed much attention to it (heck, I'd go so far to say I disliked it... but I wasn't the target audience, so the way I judged it wasn't fair), but I have to admit the designs were cute classic shoujo style at its best, and the songs were quite catchy (even translated in Spanish!).
Also, the idea of idol-like magical mermaids is quite fitting and well-thought.