We got one before our first baby was born. It seemed so much cozier to me than a crib, and the motion seemed what a baby would like. As it turned out, I ended up co-sleeping with the baby in my bed for the first 3-4 months because he'd wake and cry as soon as he was put in the Amby and wouldn't fall asleep in it.
When we transitioned him to the Amby, we relied heavily on bouncing him to get him to sleep, which was another sleep crutch. We kept him in the Amby (and traveled with it) till 8 or 9 months but he never slept well in it. Eventually we moved him to a crib, and eventually he became a good sleeper (an age thing I think). So, in our case, the Amby was no cure for a poor sleeper.
I set up the Amby for our second baby, but put almost no effort into getting him to sleep in it. Instead, I co-slept again then moved him to a crib next to our bed. I still like the idea of the Amby, and if I was really against co-sleeping, ours might have gotten more use, but overall, it wasn't worth it for us.