Learning languages can be a pleasant experience, but Iīd warn against any system that encourages speech before grammar.
I have this on personal experience with Italian and also Spanish. Hearing it and speaking it in conversational manner is all well and good, but unless you actually study the grammar properly you just donīt (eventually) realise how many mistakes you are making. I studied French at school for a long time and now, many years later, I find that reading it is not a challenge at all, as long as I know the meaning of the actual words; the sense of the thing also comes through without any problem because of the basic grammatical understanding. But, with the other two languages, though I can understand them both very well, the result of learning by ear and never taking a proper course has resulted in stilted conversational powers - not something to enjoy.
I have no idea if the Stone method works or not - all I want to say is donīt underestimate the value of learning properly, the first time. Itīs easier to learn something once, properly, than later have to forget what you picked up and start all over again. Confusing, to say the least, if it can even be done.