I used to use haywire blaster with scourges and I liked it but I stopped using them because as mentioned earlier you can buy two squads of wyches for the same price. If I were to use scourges these days this is what I would consider:
Scourges come stock with shard carbines. A decent weapon, but the range isn't very good at 18".
Shardcarbines can't hurt vehicles, so if you're firing at a vehicle, you're wasting 9 shots.
Let's look at the weapons.
Shredder: I like the shredder, but the range is 12". If scourges could jump after using it, I'd consider it, but if you're within 12" you're in charge range, and if you've ever had you're scourges in an assault phase, you'll know they're dead birds.
Splinter Cannon: This has potential. With the new rules to jink you could argue a Squad of scourges is more reliable than a venom (not better, but they will only takes snapshots in overwatch). Stationary pumping out 12 shots, with the mobility to get away from threats and pump out 17-21 poison shots depending on whether they moved and enemy placement.
Haywire Blaster: Wyches do it better. And you waste 9 poison shots if you shoot at that vehicle. Contrarily if you're firing at infanty than the shard carbines are better.
Heat Lance: Now We're talking it has the same range of the shard carbines, and if shot at infantry will hurt them. Bad. If you fire the shard carbines at anything heavily armored (2+ saves) probability says you cause .804 wounds. Heat lances generally take that up to 1.23, at least on anything T4 and below. Plus you have the option to melta tanks. Yes you're wasting 9 shots if you do that still, but it's an option. It's good to have that option in case you either lost your Anti-tank, or they're the only thing in the vicinity. 11 shots at infantry with two being S6 AP2 isn't bad. And one good melta shot with lance can bring any vehicle to a halt... Well except a wave serpent.
Blaster: Everything I said about the blaster is mirrored with the heat lance except two things. It's more expensive, and it's not melta. It can hurt tougher targets from a better distance. And if you want to field blasters, frankly Trueborn do it better and cheaper.
Dark Lance: I don't even want to acknowledge this. Heavy Weapons. Jump infantry. Either way you're paying for something you're not using, again Trueborn do it better.
So in my mind it's either Splinter Cannons, or Heat Lances. It's a 4 point different in cost, so that's hardly a consideration.
Do you want them to specialize, or be able to multitask.
I'd either start them on the table and use them as anti-infantry playing keep away with them(Splinter cannons), or hold them in reserve and use them as an all-purpose mop up unit to either remove or put a decent hole in any perceived threats (Heat Lance).
"Excess, yeah that's what we do best."