People like to play chicken with the shard bombs, because they typically aren't much of a threat. With maximum charge time reduction, Shocking Salt works well enough from what I've gathered. Scintillating Sun Shards, too. People are used to walking right over minor status with no issue, so the moderate throws them off. They work well when paired with other weapons and shouldn't be the main attraction.

Can't speak for vortexes, but they are easy to escape and avoid.

I agree with Geo about vortex being powerful in LD and I've used shards as well on occasion, to slightly less amazing effect.

Vortex
Its charge reduces movement speed making it a little tougher to place mid-fight than most other bombs, especially under gunfire. Anyone can use their jump to get out instantly, but realistically that's not even needed. Anyone can walk out of vortex if you slingshot yourself out, although that's sometimes easier said than done. But guards are also immune to the gravity effect at all times.
It's nice for zoneing and making people spend their jump before even getting into combat. Pared with a heavy weapon it can be a deathtrap. I've used it just to pull people into mist bombs because the vortex range is sliiiightly larger than the animation for vortex might suggest. And nothing's better than getting down 2-3 of these as you try to run away down a hallway.

Shards
Let me first say, the damage of the shards is not fantastic. It gets the job done, but only if the opponent really doesn't consider them a threat. Shock and stun are the way to go. I've found that placing them in sort of a triangle pattern so that the center single explosion just covers about 1/3-1/2 of the previous shards center hole is the best for a static defense. Once people show up though, you have less room to walk outside of you bomb circle than with a DBB or nitro because you should want to cover that center hole. It also takes 2 bomb charges to set up a solid defense ring against swords, so put on your dodge shoes or swap to something else if you can't handle it. It actually works fantastically if you have multiple shard users on one team, you set up fast and can usually lock people down fast enough to do good damage or kill with all the commotion. But if you want consistency, this is not your weapon... go get a mist bomb.