I like it and use it for a few reasons. Firstly, it explained a lot of the ways I am that had caused me to feel like an outsider, or "observer", fittingly enough. It was a relief for me to find that other people DO have similar motivations and tendencies of the mind.
Secondly, it's been an amazing tool for self-growth for me. I'm the kind of person who loves to challenge myself constantly and break open my own stereotypes and assumptions, so it helped highlight some ways I could continue to do that, and it also showed me a lot of the issues I didn't even realize were going on in my head. It came to me at a very timely place in my life.
Thirdly, although I will sometimes type clients that I counsel, I don't share any information about the Enneagram with them (unless they already know about it), but I find it extremely helpful with some people to figure out their type so I have a better idea of how to approach them and their issues and a better idea of what might work better with them.
I don't think it's for everyone for multiple reasons - some simply don't believe in it; some don't like to see their potential flaws mirrored so clearly back at them; some use it as a self-defeating prophecy to stay stuck where they are.