Shredder

Look at it this way:

3'' disc. (Radius of 1.5'')
Scatters 2d6 - BS relative to the center of the disc.
Doesn't scatter 1/6 of the time.
All our units who can take it have bs4.

Therefore

a 2d6 roll <= 4 is always directly on target
a 2d6 roll <= 5 still hit's that specific model on any base
a 2d6 roll <= 6 still hit's that specific model if it's on at least a 40.

A full 17.66% of the time we've hit. We also hit ~42% of the remaining 83.33% of the time this is ~35% of the time. All told this is 52.66% chance that we will hit a specific model vs 66% chance that we will hit the unit at all with a blaster. With proper initial target selections the shredder is more likely to hit the squad at large and force at least as many rolls to wound. Shredder and Blaster are both 2+ to wound against anything smaller than a space marine biker and will be accompanied by a volley of one of the following: Brace of Pistols,Shuriken catapult, lasblasters, Splinter rifles, or splinter carbines. Shred on top makes the Shredder tacitly better in terms of wounding against anything below T5, and cuts the difference in effectiveness for things from T5 to T8.

At the end of the day: sure. Blasters are certainly effective at popping marines that rely on armour saves, but almost identical against any other save, must be pared with a group of ap5 weapons of some stripe, and won't be able to make full use of their 18'' range in most cases.

At the end of the day vanilla blasters aren't particularly great AV and cost a 10 point premium over shredders and aren't always worth that premium.

It's an interesting post. First hand, I disregarded it, but after some reading, I admit there are some valid points in it. But my main concern is the following:

In our typical army, having dissies, CC reavers and grots, we already have a good threat for low AV vehicles. We don't really need additionnal weapon that damage those. As I see it, we need units to go against 1 specific kind of ennemy, while being OK against another. Against TEC, we have our dissies, that can still hurt low AV vehicles. Against small units, we have CC reavers, that are even better against low AV vehicle. Against blob, we have grots and again, they are good against low AV vehicle. Against High toughness units, we poison them to death.

I dont really see where shredder complement this army, or what they should replace.

This "typical" army didn't exist a year ago. It was february of 2015 before we really figured out how to use grotesques. Dissies were derided as an inferior choice to lances in every way and circumstance until this past spring by the community at large. Venomspam took a blaster per squad in the majority of listcrafting discusisons from the drop of 7th until 2016.

I'm going to use them in corsair lists because they perfectly synergize with Reckless abandon and the brace of pistols which in my opinion multiplies their value. I'd also have absolutely no quams about semi-suicide scourge units at 100pts.

If you use shredder scourges, it might be worth it. You get one squad for 100 points and that's not that bad.

What's your experience with them?

I've had some luck with using them on either deep striking Scourges or four on a squad of Trueborn in a Venom. In my games, I've found them to be quite good at piling wounds onto models compared to splinter weaponry. They are often more accurate than you expect and my regular opponents actually are really worried by them. They are super inexpensive for the potential damage output. I don't think they belong on Raiders though. Although with the Jink de-nerf they are better.

As I mentioned on another thread, Shredders should be good to try and bait the enemy into "conga lining" their troops, making it easy to tank shock and remove models (assuming my interpretation of the new Tank Shock rule is correct).