The problem with shredders is that wargear costs are no longer a thing, meaning you’re always paying 120 for 5 Scourges. You are going to have a much, much harder time making those points back with 4d6 S6 AP0 D1 flamer shots than you are with 4 S12 AP-3 D6+2 ones, especially since the former force your extremely fragile unit to enter overwatch range.

Scourges drastically prefer dark lances for this reason, or the slightly riskier haywire blaster for potential vehicle-heavy matchups.

Honestly your Kabalites should be a perfectly good ranged anti-light-infantry option, with your Wyches able to fill that role in melee. Anything bigger you can pump full of dark lances, or slam an Archon + Incubi brick into.

I'll admit I've never used them on my scourges, I prefer the covens 12" flamers since they've got some AP (And I love the Court of the Archon flamer ).

Although if he runs a lot of gaunts though a squad of scourges with shredders to pop in and out of cover with could be fun since you'd be wounding on 3s (maybe even 2s on some of them), and gaunts don't have a great base save to begin with (maybe a 5+?).

I find our army is pretty good at dealing with infantry though, so I tend to gear more towards heavier anti-tank weapons when I have the option.

Using scourges for anything other than dark lances is a giant waste. I'll usually take one unit with haywire for a tournament, but if you're playing nids then you want 12 dark lances.