I'm the benefits administrator for our startup (ahhh, the joys of being a cofounder) and we started before Zenefits was available. I might migrate there for the ease of management...

But I have to say, it really is hard to replace a good, responsive broker. They don't cost anything (they take the same commission Zenefits takes) and it's easy to get someone on the phone if the inevitable insurance mishap occurs. Then dealing with the insurance company is their problem, not yours.

If we started today, we would absolutely be on Zenefits. Now? I don't know if it's worth the migration.