Low cost, looks nice, simple.
Not as durable as a mounted seat, and the post could be longer.
I've owned a few. I like them. My one broke, though.. Surprisingly. Where the seat is connected to the post, it snapped. It pissed me off VERY badly. I don't even know how I did it. But aside from that I did like the seat enough to purchase two more in the future for spare parts bikes. They hold up just fine and look nice. I think for some people, they might wish the post was longer (even if just a little bit) and the seat was more padded.. but then, how could they be manufactured for such an affordable price. Overall I like this seat even though it's a 1-piece.