I think as with anything else flat fee listings have their place and they are becoming more prevalent here in my area.  I moved from a flat fee company back to a company with standard commission rates and don't think I would go back.  They present issues that sometimes are not covered with the seller like this is what you get for this flat fee but then the agent doesn't explain what happens when a contract comes in from an outside realtor asking for commission.

So, IMO I would say do it but disclose, disclose, disclose!