I love, love, love this one!
Amazon.com: Orange Pet Dog Tent Puppy Playpen...
I have it in large and it's huge and spacious for my 13 pound teapot. It has a zippered top so he's definitely well protected. It's very sturdy and I haven't seen Max tilt it at all even if he's stretching on the side. It's the only play pen I've ever had so I don't know what much to compare it to, but I absolutely think it's perfect. I'm very comfortable leaving Max in it when I leave the house.
EDIT: oops I just clicked your links and it looks like the 2nd link you listed - the blue tent size small.