Unfortunately the assumption you make re all being monthly...

Unfortunately the assumption you make re all being monthly subscriptions - opens up the other issue of customer churn.

Monthly subscriptions open up the opportunity to opt out.

Do they try for a month, 2 months or 3 months and then say for whatever reason - we no longer require the app.

This then presents another question, customer retention, customer loss, new customers.

How many of the initial sign ups are still paying customers.

How long is a customer lasting - is there a high churn. If so why?

The number of customers is important, but more important is how long are they staying a subscriber.