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Для такого рода приложения, обосновано это - единоразовый платёж.

The App itself and the description indicates that this App’s Subscription provides: Unlimited use of all content All topics with unlimited access Calculators Info graphics Charts and animations No ads Subscribe now for better results! The problem is, that you can’t even use the app whatsoever without a Subscription! The Subscription Screen (with the above noted message) will not disappear to access any content, and thus it’s a paid app, without any content use without a Subscription. It’s sad b/c I actually have other apps by this Developer.

开始时，可以免费下载使用，现在更新了，旧版不给钱还不给用了。吃相太难看。

垃圾开发者！开始就说你计划要订阅制、我都懒得下载