I've been using readlang for about a year now, and while I love the product, would never pay $25 a month for it.
It's a great product, but $25/mo is 3x more than a netflix subscription, over 2x the cost of 1TB on Dropbox, etc.
This not to mention that the vast majority of users are students and people trying to train themselves to be able to work or study in new countries.
Hundreds of dollars a year might not be a lot to you, but I assure you it is for the vast majority of people who would want this product.