The material seems sturdy but it seemed like if it did fit properly it would create bending and creasing which would be too visible under clothing. As for size, I measured myself using the guide given in the pictures, but I was able to put it on, on the smallest clamp too easily and zip up with no difficulty. There was no pressure that you would expect from a waist trainer, also I do not understand the use of the zipper/clamps as it forces the smallest level anyway. Despite using the size referencing the given pictures, I was expected to pay for the return delivery, which is 5 times what is said on amazon which I do not think is fair. On a positive note, (hence the extra star) it arrived much quicker than the estimated time, though that's on the shipping company and not the product provider.
Even if the sizing was correct, I would recommend you go for something with less mechanics and better a usability design, the claps provide nothing but extra assistance to pull the zipper up, as you get smaller, the waist trainer will loose its function and you will have to buy a new one anyway, that is considering it lasts that long.