Consider the length as well as the weight recommendations as taller babies will not fit in for as long.
I went with the natures sway (but did not need to purchase the stand as we were able to suspend from the ceiling) and it was fantastic. It can deal with a long/tall baby - not sure of the exact dimensions but it does appear bigger than the Amby. Hopefully someone with an Amby can give you some advice on their length limit, but they do look more than adequate. Bear in mind, if you don't have a particularly tall baby you should be fine.
I think that generally most babies transition out of the hammock at around the 8 month mark due to the fact that they want to roll around in their sleep. That said, some babies definitely do last longer. So you still should get 4 months of use at least. I believe that it is absolutely worth it. I used to say it was the best money we spent on
DD, it would have been worth it for even one week of decent sleep in my opinion! If you can get one on ebay a little cheaper - all the better!