What is (single controller or agents) and (controller + unlimited agents) for EAM?

What is the difference between (single controller or agents) and (controller + unlimited agents)?
For a plant to have one central ignition gateway and multiple client gateway in different geographic location. Which EAM module to purchase?

Does each client require a single EAM Module? Then what is the purpose of (controller + unlimited agents) EAM Module?

Please explain in details.

Not much details. Simply put, it’s math.

Each gateway requires an EAM module to act as the controller or as an agent. At current pricing of $18900 USD, that would be a 14 unit break-even point.