Thanks, it hadn't occurred to me that the app stores would enforce easy cancellation. I'll remember to prefer in-app sign up over website for any new subscriptions in future.
I feel the success of small developers relies on IAP, it means I can purchase from them without needing to trust them - the app stores do a good job of reviewing the app for malware and if the app doesn’t live up to expectations it is trivial to get a refund from the various app stores.