I think the right initial metric is “do any users love our product so much they spontaneously tell other people to use it?”
Many larger companies use "Net Promoter Score", as a way of telling this:
https://en.wikipedia.org/wiki/Net_Promoter
Of course, like Agile, there are Consultants, a methodology and books, but there is some truth in asking your customers if they would promote you to another person.