I had the same question. It's a shame that the site doesn't have any additional information or links.

I'm also hesitant about the price... for $10 a month this service should support a large variety of languages and offer a lot of in-depth questions for each language. I can get the same knowledge elsewhere for free, so if I'm going to pay for this, it should be worth it.

Agreed, that's the first question as soon as I saw the concept.