[yiyus]

It depends how you define success. It is indeed a remarkable achievement to have survived this long and have a (growing? I think so) speaker community, and I could agree it is worth learning. But the goal was not to just work, or have a small community of speakers. It aimed to become a world-wide known language for international communication. In this sense, it would need to have an importance of the order English has today to be considered a success, so I think that "not very successful" is even a bit too generous.