[zafiro17]

Noom, a popular diet/weight-loss app, works on the same principle. I've used it. To start the free trial you need to prepare the payment mechanism. Then after X amount of days, the paid service automatically kicks in. I wasn't super-excited to discover I'd just committed a lot of money before I was ready or even fully committed to the app/service.

I suspect this is going to be the new trend for future apps, since it almost certainly delivers a higher number of paid users than other methods do.