Major advantage is frankly its price.
What you get:
Several tetradestic or pesudo-tetradestic (somewhat tweaked) stacks, with formula for card-number and number-card conversions, as well as prior/latter card. As advertised.
A super-brief introduction of Unknown Mentalist's concept, Clock Principle, with permission. Guess there is some underlying algebraic structure, some sort of group or ring or something that remains undiscovered, but I am not that much of a mathematician to find out what. As the Clock Principle underlies UM's popular manuscript "Karma Stack", it might be said that you received some essence of that ebook with kind permission.
What you DON'T get:
The "shadow" concept itself. Dr Solka gave examples so I managed to figure out much of how the shadow operates, but that is no replacement for a real introduction. I anticipated a monologue or at least a paragraph discussing the shadow, so readers may judge if full research into the concept (discussed in Solka's other work "Im Schattenreich der Spielkarten") is worth the effort (mind you, that book doesn't have English translation, at least not available on lybrary!).
ACAAN calculations. Admittedly, the advertisement didn't say this, but Mr. Larry Finley in reviewing "Si Stebbins Pro" by same author, pointed out that "a shadow stack such as 7QS or the Sequoia stack" facilitates quick ACAAN calculations. I mean not the slightest offense to Mr. Finley, but this manuscript about the shadow sequoia stack DID NOT introduce ACAAN calculation formula. It is possible that I misunderstood Mr. Finley who referred to something else, or that said formula exists but was hidden in the shadows of Im Schattenreich der Spielkarten. Pun intended.
Non-rotational suit arrangements. Not that I care much about systems that tamper with rotational arrangements, for these often burden the calculation, and a real memorized order (Mnemonica for example) would be better if your routine, like the Nikola style of restoring order from shuffled pack which involves CALLING OUT order of cards, puts the sequence under fire. Yet, a brief introduction or discussion would make the manuscript more comprehensive.
A stack that "stands out". Tetradestic stacks with card-positon and position-card calculations are not rare in the magic literature, and this ebook does not disclose much information that makes its stack superior to, say, the Karma. As I've said, such advantage may do exist, but saidly is not present here.
So basically, if you just want a "card _-_ positon and prior/latter card" stack at a low price, this is a decent purchase. If you are interested in reverse-engineering and discovering properties (instead of incorporating them into your stack), this may also be worth exploring. In other cases, I kindly advise caution.
Alex.
