How to use shard bombs effectively...

Does anyone have good tips for using the shard bombs effectively (Other then simply "use other bombs")?
I recently crafted a Deadly Crystal bombs hoping the 5* version wasnt as wimpy as the 4* one and that it had some hidden mechanic or tactic I didnt knew of, but even with Very High Damage bonus it isnt that great. I get that you are supposed to hit with multiple shards at once but with some enemies is hard to time it (sometimes just the central explosion hits and nothing else or just 1 shard explosion connects), only been really good at it after using Electron vortex to reel monsters in... only to have the monsters fly everywhere in odd directions for some reason.
Maybe I am using the bombs incorrectly or maybe there's something about them I am missing but the new ones (used to have sun shard before the patch changed them, sold it soon after in disgust but some time has passed now so I want to give these bombs another try) so I'm asking for advice from you guys.

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.
I see shard bombs as a compliment to a gun party, and a nuisance in a sword party due to the unpredictability of the knockback effect.
Unless you solo, even then without CTR max or damage max it is somewhat useless.
I recently ran JK with a shard bomber.. what a nightmare. I stopped using my sword and switched to guns. At other times switched to sword and stayed as far away from the bomber as possible, killing 1 or 2 monsters in my own corner.
If you want to get more efficient at placing, that is kite practicing. Same with haze bombs, if you want to hit the monster with the initial blast and also catch him in the haze, then time it correctly, the focus is on the center. With shards the focus is just on the outer ring, if you want multiple shard hits. (Max 3)