This is what I was told. It is water resistant, not water proof. I would not scuba, swim or bath with it. However, it should survive sweat and short contact with water. I would recommend going to the fitbit website to get the company answer. This is the same answer given in the community and the sales rep.
The major difference is that it is the first device to track heart rate and duration. I think this is important. The higher end smart watch does the same, but it has a bigger display.