Firstly, why would any barbarian take Hurl Weapon over Improvised Missile when they do almost the same thing, but Improvised Missile does it better?
Second, what exactly do you get out of it when the weapon can now be used as a Heavy Thrown weapon? Obviously, it now has a 5/10 range and you use your STR on the attack instead of DEX, but does this also mean it now does normal weapon damage? After all, despite the fact it was an improvised (or off-hand melee weapon), I am now using it as a Heavy Thrown weapon so it should do normal weapon rather than improvised weapon damage. Will a magic weapon used with this feat return to the users hands after the attack?