After saying all that, I'm probably going to surprise you now by saying that in my personal opinion: the illustrations in these books stress me out MORE than what I was before I started thinking about colouring them. As you all know I dislike geometric, monotonous, repetitive patterns. What relaxes me most is illustrations with a theme or content that means something, rather than lines, boxes and random objects.. It's just boring more than anything, and a lot of the pictures in these books are sharp angles, or the same thing overlapping each other hectically... it's just all too busy and too tedious to make me enjoy what I'm doing.
The thing is, as with everything in life, different strokes for different folks. The person next to me might look at these books and think, 'hell yeah, groovy geometrics, cuboids, lines... love it!' so if that's your bag, I guarantee you'll love these books and recommend you try them.
The paper quality is not bad. I used stabilo felt pens and there is very little bleed through to the other side unless you press down hard. Each book contains around 25 drawings and an introduction telling you all about the scientific Alpha/Beta brainwave system and how colouring can manually 'change the gears' of your mind's state.
Here's an image I coloured from the first book. I don't like how narrow the lines were as I ended up going out of them a few times!