As everyone else has said, these are utterly ingenious and probably my favorite magic purchase of
the year. Critically, I think the reviewer who suggested these are really only useful for the
effects included has it very much backwards: The effects taught with the trick use only the marking
system and assume little or no knowledge of sleight of hand, which makes sense. But the real power
of these isn’t as an sole method for stand-alone effects (excellent though they are). It’s making
everything else you do an order of magnitude stronger & more impossible. You could, for instance,
let a spectator shuffle the cards, then “set up” another effect that requires a particular
arrangement at the top, without looking at the card faces. Change an indifferent card to an only
verbally selected card in the spectator’s hand (and, more generally, turn lots of “pick a card”
effects into “name a card” effects). Basically, think of any effect you do and ask “how could I
make this stronger if I could instantly (well, very quickly) know the position of any card or cards
in a shuffled deck?” The more sleight-of-hand based card magic you already do, the more value
you’ll get out of these.