Works for us, anyhow. We have a clear mission, but the vision of the product is constantly evolving. The CEO/head of product does have final authority, but we are all definitely involved, and I think it's a very collaborative process.

It helps that we work very incrementally and are very data driven. Every commit goes live after the unit tests pass, and we commit every few hours. We don't have to agree on everything, just the thing we're testing next.