Ah! I had no idea what you were talking about until I googled it. They have them in every park in Korea, they are so much fun!
It takes you a while to get into the groove of using one, but its really easy to up the intensity, you just have to take longer strides.
I find them to be quite fun. I don't know if its quiet or not, the only one's I've used have been out of doors, but they are really smooth and easy. So go for it!
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