How many types of people do you think would benefit most from this product?
How many people have you recommended this product to?
Retention Rate? (Percent of customers who continue to pay you over a month.) Compare with your competitors. The rate varies from business to business.
How much room for improvement does this product have to better meet your needs?
How disappointed would you be if this product no longer existed tomorrow ?
How highly do you value the primary benefit you have received from this product ?
How many alternatives to this product can you name if it were no longer available ?
Adapted from "Hacking Growth" by Sean Ellis and Morgan Brown