The concept is great, very practical and clean. I've watch Andy Leviss perform it several times (as a demonstration to the gang @ the 72-Hour Gathering) and can only say that it's "clever."
(Yes, you do hear a "However")... unlike the majority of things I've purchased from Lee, I believe SB to be a bit stiff when it comes to price, given what it is and how inexpensive said "substance" can be obtained. Too, as I understand things, it's not the only effect using this technology.
Effect wise... you can't beat the seeming impromtu advantages this stuff delivers when it comes to doing a serious Booktest demonstration. You can literally walk into a bookstore and allow them to select ANY BOOK... the odds are 99.9999% to your favor.