I currently just use shivermist to make it easier to hack up opponents with my sword, but I was considering getting a radiant sun shards bomb. The fact that it only goes up to four star is a problem enough, but I was wondering if facing a different direction would change the directions the 8 shards came out in. Then I would be able to alter the aim by 45 degrees.
Crystal bombs will fire shards in all vertical and horizontal directions as stated. Regardless of your facing direction they will always fire in the four cardinal directions plus the diagonals between them. However for pure bombers (though I guess you probably aren't one) this is helpful when using it to snipe Gun Puppies.
In truth, in it's ideal situations it shouldn't matter precisely which way the shards fire. The idea is to have it placed so that monsters are standing on it when it explodes. If you can do this reliably, the 4-star limitation is not really an issue as it deals huge damage when you hit with multiple shards. It is excellent against lunging or charging attackers such as Greavers and Zombies, and in combination with Shivermist you can effectively use it against almost anything. However it remains situational as against single monsters or ranged attackers (hello Devilites) it is difficult to use.
Just don't go for Ionized Salt Bomb. The charge time is at least twice as long.