Not and experienced shardbomber here, but I have experimented with the 2* versions (and watched a good amount of Shard Squad). From the limited time I have had and reading other stuff. shards start to have bugs when you hit enemies with too many shards. Adding to this the fact that the bright explosions cause some lag and distract teammates, and I would say that shard bombs are definitely not for the weak-of-heart.

Explain to me why I would ever want to use shard bombs over ash of agni or voltaic tempest, provided the enemies that I am fighting are not immune to both, and that none of my team mates are bombing in the exact same manner as myself. i.e. three shard bombers all running away from enemies would probably outdamage ash of agni. But that scenario as the big reason to get shards over haze bombs is kind of cheap reasoning-- few people use shard bombs seriously, and even fewer people want to play the role of damaging support bomber often enough and outside of arenas.

Nitro, Dark Retribution, and DBB cover damage dealing, though DR is DLC.
Knockback from the second set of shards really make shard bombs hard to use safely.

Might pick up a 4* Salt bomb out of boredom, they seem to work like DR but with a fuse on the projectiles.

"Shard bombs are already outclassed in terms of damage (we all know this), making voltaic tempest/ash of agni the better option when fighting an assortment of enemies?"

No. That is just like saying FSC is the best place for farm crowns (we all know this) [it actually isn't].
Just because you don't know how to use them yet does not mean they aren't useful.
As I've said in other threads they are excellent defensive bombs that deal faster damage to slow enemies than blast bombs or can add in a status to the damage.
Holy-Nightmare said it fairly well: "Shard bombs do have bad damage [snip] but they are not made for standing relatively still and chainbombing. Shards are made for the highly mobile bomber who wants to run, do damage, and not get the monsters that are chasing him blasted into him."

But did you know?
VT deals super little damage with the status and only really acts as a shivermist for ice themed monsters?
AoA's only real good use is melting the ice cubes?

The big problem with shard bombs is that they seem to have a hole in the center of their blast pattern. You know, right where you're standing, and right where enemy will try to get. And since shard bombs take longer to actually explode, there is a good chance that enemy WILL get there. More than once I've seen zombies jumping straight into the middle of the shard ring and staying completely unharmed by the explosion.

So I agree that DBB is the most newbie-friendly bomb. I've started this line after playing with Sun Shards, and found it superior - DBB line allows for good movement speed while charging, has nice solid AoE and decent chance of flinching, plus it explodes faster.

I thought there was a bug when more than 3?4? shards (incl. blast) hit the enemy, the shards don't function properly anymore. I was messing around on an alt and found that even though I should have huge damage when like 5 shards hit a GLC, I didn't have much. So Vana took all the shards? I may be wrong, but that doesn't seem right.

@Skeptic

I was talking about dark retribution and dark briar barrage, not the blast bombs. And please, tell me how to use them.

First, mobs can only react so fast to you. Continuing example with zombies, once a zombie began preparing for the jump, it won't change the direction of the jump. And if you happen to place the bomb just before that, it's likely to jump straight into the safe zone where you were standing. Same with other mobile mobs. That hole is still a liability. Yes, it can be counteracted, but it's the need to counteract it is what makes shard bombs inconvenient. Since there are other bombs that have about the same (at least it feels so) DPS yet don't make you worry about the blast pattern at all, why use shards?

Leaving trail of destruction? Regular bombs can do that just fine, (well, those without huge knockback at least), plus shorter fuse means you can wear down faster enemies that way, as they are less likely to cross the blast area by the time bomb actually goes off. So you can use them both for area denial AND setting deathcourse, while only having to worry of not running into attack. Other bomb types seem to be more of support role, though I do agree they are extremely useful in certain situations.

Now that as @Jenovasforumchar noted, shards could be useful against those towering bosses, especially ones who like to rush towards you - they will get hit by the shards anyway, despite standing in the hole. An example would be giant Lichen Colony, I suppose. But since there said to be a hit cap on shard hits against one monster, a good chunk of potential damage is lost.

Grievers are not handled by shard bombs very well [sun shards exception]. They are too fast. A skilled bomber can kill them with shards, but most bombers will have difficulty unless they have help in the party.