Complete bait and switch. I originally purchased this app as part of a $4.99 bundle alongside the sit ups and crunches apps. It was sold as a simple one time payment with no ads and no subscriptions. Then the developer quietly pulled the apps from the store, making it look like they were discontinued, only to relist them later as subscription only. Stripping features from existing buyers to force a recurring fee is completely unacceptable. I feel like I completely wasted my money, and who knows what else this developer will lock behind a paywall next. Save your money and look elsewhere.
If you bought the app before it went free, you still get everything, no subscription needed. Open Settings in the app, scroll to the bottom and tap Restore Purchases, using the same Apple ID you bought it with. You shouldn't have needed to do that, so I've fixed it for the next update: the app now checks your original purchase with the App Store on its own and unlocks your access automatically. Any trouble, email me at support@ludyem.dev and I'll take care of it.