What are some alternatives?
When comparing Crystal and StopAd PRO, you can also consider the following products
BlockBear - Block ads and protect your privacy on iOS with a bear
Adblock Fast - A faster ad blocker for browsers and iOS 9
Goodly - Student loan repayment as a employer benefit
Brave - Fast and secure, ad and tracker blocking browser.
Ourdata - Block ads or unblock and get paid or donate to charity