I have one of these. It works but it is more of a novelty than a practical device. I like odd interfaces for my Atari computer so for that reason I keep it. Complete in box is a rarity. I have seen 3 or 4 come up on eBay this year but none where complete. I cant tell from the pictures if the "Relax Stress Reduction System" book is there. It is a spiral bound book. The cassettes are the equivalent to ASMR today. This is also odd in that it included the software and interface to be used on The Atari, Apple, Commodore, and IBM right out of the box. attached is a review of the Relax System.
Synapse Relax Review.pdf