This isn't for every mentalist, but in the right hands, with the right presentation and audience management, it can be amazing. Yes, this ebook is on the pricey side--and if you decide after you buy it that the technique isn't for you, you'll feel burned. I'll try to help you in your decision. First, this isn't for novice or beginning mentalists. This is one of these propless concepts that the top UK mentalists are so good at, something that takes practice and care in performance. You have to have some audience management skills; that is, your spectator has to follow your directions explicitly; otherwise, you have big problems. Also, I think some of the extended ideas in the book are basically unworkable--or at the very least, dicey--in practice. Lastly, it's not 100% foolproof, nor is it going to baffle 100% of the folks 100% of the time. A really astute spectator with a good memory could try it later and with some thought reverse engineer it.
Even with all these caveats, the underlying principles are, quite simply, unique and brilliant. I use air writing for exactly two things. I do a "which hand" routine. I end with being able to say whether the spectator has thought of 0, 1, 2, or 3 coins in his hand. I also can divine a chosen ESP symbol. OK, so I'm not using the principles in the book to their fullest extent, but I have developed a strategy is accurate and one that works well for me.