Good Find and thanks for sharing it.
Looks HARD. That type of foam is much denser than the Nerf foam.
Looks quite a bit heavier than a standard Nerf. The shaft (hopefully hollow) looks to be hard plastic on the outside going though the bulb and extending all the way to the button tip. If so, I wouldn't want to be hit with one.
We need more information. Does the seller post it? Link to E Bay please.
I would question its safety until we have more information about its mass and construction.