It does not dry hard. It's kinda like a tuff marshmallow in texture when dry.
It is meant for grade school children and in class modeling, it's non-toxic. I have found it on eBay but it comes in boxes of 75, 4oz packs and is around 140 bucks for the box. I had a clandestine method of getting the stuff. I have found putting the opened air tight pack into a zip lok bag has kept it for several months. I made this raft thingy from the same bag I made the insulated interior wall cover for my SH-3A helicopter. So it's kept pretty well.
If I want something hard and workable, the Miliput is the thing. Like I used on the mod of the wheel pontoons for the SH-3A helo.
Hope this helps to clarify its use.