Elephant apples and cannonball trees are in yards and gardens around here and these 2 species seem to be large trees that look kinda ok but the are not too many other redeem ing qualities.
Cannonball trees are spectacular when in bloom and also when fruiting. But when dropping fruits they will stink up your yard and take lots of space. Not for small yards. Fruits not edible, by my definition of edible.
Elephant apple is edilbe but needs some preparation. They are used in curries in India. But i've never tried cooking them. These trees can also get quite large, but not as specacular looking as cannonball.
If looking for edible fruit much better off going with quaribeas (aka matisia).