Costly effect that needs a specific type of monster to use.
You can tribute Throwstone unit to activate his own effect. But in this case Exiled Force is an overall much better card because it can be used to destroy any monster face-up or face-down, and no matter the monster's stats.
The range of monsters Throwstone Unit is able to destroy depends on his attack stat. To be able to destroy a wider variety of monsters use effects to boost Throwstone Unit's attack. A good way to do this semi-permanently is with equip cards.
Throwstone Unit has a considerable amount of defense, but what he needs is attack stats to make him and his effect much more useful. Use effects that switch the attack and defense stats of a card, with Inverse Universe being the best.