We have an Amby and it worked very well for a period of time. At some point (probably about 9 or 10 months), DD decided it was too confining for her and she wanted to be able to squirm around. So that was the end of the Amby! I am planning to break it out for this baby, though.
I believe the Amby has a weight limit, not an age limit. The exact weight limit is on their website, and you can add an extra coil to hold extra weight. It is very low to the ground, so you don't really have to worry about them climbing out. But as I said, our problem was that she just wanted room to flip flop at night, and the Amby wasn't giving her that.