Encryption is done through convergent encryption (example here: https://news.ycombinator.com/item?id=7601277).

We do offer unlimited storage for $20/month, the 200GB for $20 is what Dropbox offers -- sorry if that was unclear.

Oh right!

Thank you for the clarification, it might be worth re-wording it slightly on your site? (or maybe I'm just blind!)

It looked like they were just doing a comparison to other services like Dropbox which give you 200GB a month for $20. They have a section stating it is truly unlimited due to compression algorithms and stuff similar to what Mega.co.nz tried to do.