Yes. They are a referal service. They find potencial renters / buyers and refer them to agents like I. The only difference is that they don't handle your case directly but the agent they refere you to does. For what they have the agent pay them a refereal fee. So you are better of going to an agent directly such as myself.
I would be happy to assist you in finding rentals in the nw suburbs of Chicago. Feel free to contact me directly. A leasing agent is typically paid by the owner/landlord, so there is no cost to you for using their services.
Red Fin is basically a syndication site that posts homes/rentals from the MLS (with limited data). They have some nice data, but they don't have anything more than Realtor.com, which does the same thing.
Talk to an agent, who has full access to the MLS at real time, and they will be able to help you.