The open listing is mostly used by individuals trying to sell their home by themselves, who are also willing to work with local real estate agents. Basically, an open listing gives any real estate agent the right to bring their buyers on a showing to view your home. If their client purchases your home, that real estate agent earns a commission. There is absolutely nothing exclusive about an open listing and a seller can give out such listings to every real estate agent who comes knocking on the door.
For that reason, it’s doubtful that any agent is going to market your home or put it in the Multiple Listing Service if it’s an open listing. If your home fits the criteria for one of their clients, and it is convenient for them, they may be willing to show it to their client. That is really all an open listing is good for.