You came to the right subforum.

I've done a lot of research on these bombs and as such I have a lot to tell you about them. The most important advice I can give you is that cooperation is everything for shard bombs. If you have a teammate who is not supporting you with his own bombs, chances are your shard bombs will disrupt his flow. He'll get agitated because the knockback will mess up with enemies in the area in unpredictable ways. His first instinct, being surrounded by all this chaos, will be to get the f- out of dodge. This can lead the enemies away from your bombs, letting you have little impact at all on the fight while your teammate won't be attacking either because they're busy trying to run away from the chaos you're causing.

Don't let that happen.

If you're solo, planting the bomb repeatedly on the same spot and kiting enemies into the danger zone is the best way to go for damage. By hitting enemies with the core + 1 shard, you can almost reach the damage levels of Nitro and DBB. Sometimes you'll get lucky hits with a second shard and that'll bring your DPS above those. Since the bombs have much less knockback and a bit more interruption than Nitro, they could end up a bit more effective. If you use Shocking Salt or Scintillating Sun, you're also distributing status, adding to safety.

Another tactic is to kite enemies like you're using an Ash of Agni. I favour this tactic against Too Many Devilites. You can hurt enemies while giving them a very wide berth, an advantage not offered by the quickly-detonating Nitro and DBB or the slow-moving Irontech and BAB.

If you're in a team, the optimal condition is if your teamates are also using bombs. Sharding inside a Voltaic Tempest is great. Sharding inside a Stagger Storm works out. Shivermist is absolutely fantastic to shard inside, and those work just as well as Vortex Bomb. If someone can alternate between Vortex and Shivermist/Voltaic, you're basically just cheating your way through the stage. All the enemies will be gathered in one spot where you can inflict massive damage upon the whole gang. It's possible to do this combo on your own, and I used to stick with that for a while. Plant a Vortex, lock them in place with Shivermist/Voltaic, lay a couple of shard bombs, they'll be dead.

The second best is if your teammates are using non-knockback guns. That means no Polaris. Alchemers are fantastic to cooperate with. Blitz works out nicely because the Blitz can hold enemies in place. Antiguas are alright too.

If your teammate is using swords, sit down with them and have a long talk about strategy. Tell them to lead and knock enemies into your bombs. Stick with Sun Shards and Shocking Salt so that your teammates are safer inside the chaos of your shard bombs. Maybe bring a supporting haze in addition. If your sword-swinging teammate doesn't cooperate with you, you might as well find some corner of the room and /sleep for all the good you'll be doing for the party.

Edit: Oh, and see if you can find fellow shardbombers. A team full of shardbombers is the most amazing thing.