I am not a true licensing guru when it comes to stealthwatch. I know up to 250 exporters that will be close to 4,500 flows per second. But is there a true calculator out there where you can plug in the number of switches/exporters to determine the number of flows per second a customer needs for licensing?
If your customer doesn't purchase Stealthwatch yet, I recommend them to use an evaluation license(PoV) in the production network. Flow Collector can show true Flow rate in web UI. Of course, UDPD also shows Flow rate too.
Or if your customer is a certain volume customer then there is another option as EA(Enterprise Agreement). In EA, the customer doesn't need to care about Flow Rate.