First of all, I love the FitFlop technology which has helped tremendously with chronic pain in the ball of my foot. I fell in love with the summer flipflops first and now, after moving to the East Coast, was glad to find a winter boot that would also be good for me. Two things that would improve this product for me are: 1) half-sizes up into the high numbers. I wear a 10.5 shoe and even though the size 11 fits pretty good with the double winter socks, they are still a bit loose at the ankle.  2) a side or back zipper would be much easier than the pull-on style, especially with aforementioned socks and possibly pants tucked in.
Other than these two points I am happy with the look, the feel and most of all the comfort of walking without pain.  I cannot speak to the toning properties, but perhaps I will notice some change in the months to come.