Beings of Tash Kalar
Note the exploding effect does not only destroy the summoned piece, it destroys also one of the pieces used for summoning the Bomb, if common. Thus it is better if that piece is upgraded or even not yours (using improvised summoning in a deathmatch melee).
Also note: It is not necessary always to use the exploding effect. You still can destroy one common piece by summoning the Bomb and you do not lose your own piece. Sometimes, you can even benefit from the fact that it fizzles. It is an easy pattern and thus easy to fulfill "summoning" tasks. As your last action, you can safely summon it on a colored space in the midst of your tokens.
Also, originally, the Bomb exploded regardless of the timing. It was a bit annoying for the opponent, as it was too easy to set up and thus hard to prevent even if it was expected. The fizzling option added nice tactical options and made the card much more interesting.