I have one of these. Only used it twice - once for a picnic, and once to sit on our garden bench yesterday! Bum went a bit numb on the bench, it was comfy on the grass though. I've got it for a festival as I have crap posture and tend to fold in on myself if left to just sit on the ground. It has a pocket on the bag, which might be handy, and a shoulder strap (which realistically you have to unclip to sit down, but does make carrying it easier).
That looks like a better bet for the pregnant person tbh. And with the one I have - you can sit on it cross-legged, you can sit on it with your legs out flat. You can even sit with one leg out straight and the other bent at the knee (in a jaunty fashion). But if you try to sit with both legs bent at the knee you tip over backwards and end up with your legs waving in the air.
That does look better, but I'd get annoyed carrying it. I've got a camping chair already, but I don't want to be carrying it, or worrying where it is, when I'm dancing. I think I'm going to have to go to some shops, try a few different types out and see how practical my first choices are when I'm pregnant.