Is it wise to sign a non-exclusive buyer agreement with an agent?
Well, if you do you better make sure you use that agent to buy a home. Some agents only have their clients sing one once you are ready to make an offer on a property.
Are you looking to work with other agents as well or just them? A lot of times the agent is just trying to get some commitment from you that if they spend time trying to find you something, you will be loyal to them. If you are going to work with multiple agents, then better check the wording of the agreement. For example, if the agent sends you a list of ten properties does that mean he represents you on those just by sending the list? It could get messy. Best to work with one Realtor you like and trust, then the non-exclusive buyer agreement shouldn't be an issue.
As an investor, I wouldn't sign one. I want as many quality leads as possible from as many agents, brokers, property managers, etc.
In my state the laws prohibit you from disclosing anything that may go against the seller unless you have a signed buyers agency agreement, otherwise we always represent the seller in the transaction. This might not be the same in your state. As Louis said he probably wants some sort of commitment before he starts putting to much of his own time into it.
Call another agent that specializes in investment properties in your state and see what they say.