I have used this at my gym. People who say it is more of a workout because it doesn't have a motor have NEVER been one on and are just saying what sounds logical.
It is like a hamster wheel, like the videos you see when the wheel gets going too fast and the hamster does a couple revolutions glued to the inner wall. This thing move SO effortlessly when you are on it. It makes you feel like you have to keep going a bit faster and faster to keep up. As some have said it is very easy to speed up, not so easy to slow down. I felt when running though I was in control, but maybe right on the edge of control. I always had to use the handles when slowing down though or just hoped off to get back to a slower pace.
IT IS built solid as a rock, way more solid feel than any other treadmill I've been on, feels like running on a solid surface doesn't flex and give like the deck of a regular treadmill. That is not to say it is hard on your knees etc because of the curve shape I felt no leg pounding or stresses.
All that said, I actually like it a lot and after using it just a couple times I got better at it. If I use it more regularly I am sure it would be great. If this thing was like $1k or so I would definitely get one, but at the price they want... NO WAY. I could get a couple different quality pieces of equipment for that cost.