It is generally accepted that the agent who HOSTS the open house is entitled to the leads and buyers that attend the open house.
Since the agent that sits the open house for you is not directly compensated (in other words, is not paid a salary or a fee) any leads, whether they are for potential buyers or sellers, would go to the sitting agent. According to studies, a fraction of a percent of listings sell to an unrepresented buyer walking into an open house. Since so few listings sell in this manner, why do agents hold them open? The answer is personal/brand exposure and to gather leads.
Since the agent sitting the open house is putting forth considerable effort to market your listing to their sphere and drive traffic to the open house, it is only fair that they get the leads as the result of their hard work.
Of course, as in all things related to Real Estate... it's negotiable. Agents4Opens invites you to have that discussion among yourselves prior to the open house. This will help alleviate any potential for a misunderstanding.