The Gemini Principle will be of interest to those who enjoy collecting propless, gimmickless "which
hand" effects.
That said, I'm not sure I would call it an improvement on extant methods.
True, the gemini procedure is simpler for the spectator to follow than tricks which rely upon the
truth/liar premise (which this abandons). But I'm not sure "simpler" is necessarily a good thing in
a trick like this; especially since, to my mind, the spectator "feels" like they are helping you
solve a puzzle rather than actively deceiving you.
Indeed, the strongest effect in the
booklet uses another well-known mentalist technique to conceal the Gemini procedure from the
majority of the audience members--yet this technique requires even more audience management than an
effect like Tequila Hustler!
So, if you are a serious collector of these kinds of things,
then perhaps it's worth the cash. As an enthusiast, I don't regret my purchase, but as a performer,
I don't think I'll be using the routines included here.