I like them. My mother does too. For sitting or laying on. But it's not for yoga. If you asked for a yoga mat and that's what you need then you can ask for your money back since the seller doesn't know what he's selling. The producer is definitely a commercial operation but for all the claims of health benefits, I personally go by a simple "what you see/feel/taste/smell/hear is what you get" criteria: If it feels good to sit on it, that's the benefit, and if you're ill, see a doctor.
On the "feels nice" gimmicks topic I can recommend something for the head too, like these