I don't know much about didacts, especially teaching foreign languages. But i'm not sure whether there's really a "system" behind that site. It mainly offers translations, some sort of "language in context / in action". This makes it easier for someone who already has some acquaintance with the foreign language to broaden his/her knowledge regarding vocabulary and formulations.
But grammar seems to lack completely. The focus of that site is vocabulary and "multimedia" learning, seeing and listening a certain word or phrase in different situations and circumstances. This may aid vocabulary memorization, but i fear the learner will stick to that phrases if that site is his only resource.
So, IMO it's a neat site to complement a systematic training, but not to substitute it.