I have purchased this app a week ago and yesterday I published the app. Here is my review for future buyers and my recommendations for developer to fix. I would change my score if these will be fixed and a new version is released.
+ Code quality is very good. Database is managed with Room Persistence library. Awesome!
+ No obfuscated files, no stolen code as far as I seen.
+ above average UI and very well structured project
- Please remove your JKS keys from gradle file, and also please set minify and shrinkResources default to true. I hope your published demo is also shrinked, or the source will soon be all over the internet.
- There are no guides. I wish there was at least 1 guide for premium feature setup.
- Some strings are duplicated unnecessarily, such as admob id, ad unit id etc. Those can be set via translatable="false" attribute
- Please use arrays for string arrays in next version, When adding a new currency you have to update all string files....
And Most Importantly!!
- Google play billing api is old, please see; https://android-developers.googleblog.com/2020/06/meet-google-play-billing-library.html
An important notice on this: Starting August 2, 2021, all new apps must use Billing Library version 3 or newer. By November 1, 2021, all updates to existing apps must use Billing Library version 3 or newer.