In the next update free users will be able to store one test log entry so that the calculator pages show your last tested / saved values and so that you can see what you'd get if you upgraded for unlimited test log data. We think this will make the app function more intuitively for free users, and offer more value for free of course too! We are definitely working on adding more features for premium subscribers to increase the value of paying for it.
We don't store data in iCloud since we want users to be able to access data from any device. Many users (including myself) have devices in multiple eco-systems, and when I first started working on this app, this was a key feature for my own usage. I want to be able to access my data on my Android phone, iPad, and windows desktop (coming eventually!). Unfortunately Apple does not allow iCloud data sync from non-iOS devices
so it wasn't an option.
We may eventually allow an option not to sync data, however there would still be some subscription cost associated with the app IF we ever did that. Let's face it, recurring revenue is required for recurring maintenance and new features. There's this illusion that apps can be sustainable as a one time fee, which simply isn't true. We had a number of options when working out pricing. We could have created a new version each year (eg: Pool Math 2018) where you had to buy it again to get new features, or we could just let the app die when sales stopped. We really felt the best option for everyone was a subscription model. We'll definitely keep looking at other pricing structures in the future, but for now it seems to be working, or at least generally allowing us to focus on improving the app.
Apologies if it's too steep of a price to pay, we are simply trying to make this a long term viable project. Hopefully at some point in the future you'll re-evaluate the value of becoming a subscriber!
Thanks!