I'd be very wary. It appears this is along the lines of the old "10 tapes for 1 cent" scams back in the day (just dated myself a little, right there!). They keep sending you books you didn't order with an invoice... many comments in the above link suggest the product testing is a lure to get you into the club and few folks get anything worthwhile. My guess is they have a warehouse full of very cheap stuff they send out for "testing".