It's good to get a feel of how the language basically sounds and feels like. But it's only a basis from which you can develop. Sure it's really expensive, and I don't really know if it's worth the price, but if you have a chance to get it, just try and decide for yourself. And I also think you can use it efficiently without a grammar guide of some kind (but I think I mentioned this before).
But you also don't learn a language by just learning grammar and words. You have to learn sentences. Not to translate them, but to understand without translating.
Just my opinion.
Ah and a bad thing about RS (Japanese) is, that they speak veeeeery slow. I don't think you will meet any japanese person speaking this slow
There's also another page for learning with dynamic imersion. It's called live mocha and large parts are free. It's not as good as RS though.