I lived in the Caribbean for a few years on various islands. Locally these are just called bread fruit trees, I think the author made up the cannonball thing from the sign, people often put funny warning signs up on these trees.

It's a basic starch staple like potato or rice for people throughout the islands. It has a mild bland taste with a bit of mild bitterness at the end. However, it's plainness makes it very versatile.

It's made into casseroles, seasoned, meat chunks are added when people could get it, think funeral potatoes for a similar taste and texture but it needs boiling down to create a kind of mash to use in other things like casseroles.

And yes they are also dangerous, I have met people injured by them and stories abound of people killed too. A highly superstitious area, people had all kinds of metaphysical reasons if you are hit but usually it had something to do with too much rum and not paying attention.