It does seem odd that a web site supporting owner sales would let agents in the door, but I never thought I'd see agent advertising on the floor of my local grocery store, either (feels odd running over an agent's picture with the cart...). Perhaps the owners aren't a strong enough revenue stream. There are 11 agents signed up with them in all of California.
I'm going to pass on this marketing channel for now.
They aren't always easy to convince, but they are potential clients that you know want their house sold. If you can create a listing presentation geared towards their needs and concerns, it can be a great way to get listings.
I would think the return could be there and if you want listings, it may be better than Trulia/Zillow where I think the majority of leads are buyers.