Originally Posted by
OXRS
Most of the time you'll never target vehicles, but when you fire four large blasts there's a good chance you can catch one in the blast. Also, when you target a vehicle you can place the centre over any part of the vehicle, so if there are multiple infantry units near the vehicle it's possible to get more hits in that way. Either way, if you glance a vehicle it won't shoot next turn. That's one in the win column. Besides that point, you're shooting four of these missiles so there's a good chance you will get a penetrating hit in which can remove a weapon or immobilize. Shatterfield missiles do that better than monoscythe and necrotoxin can't do it at all. So no, I don't agree with you that you should never target vehicles. You should do what is tactically viable at the time. If the vehicle is your only target then it is a huge waste of missiles, but that's a gross over simplification.
Your funny point isn't so funny. First, 5+ armour saves are irrelevant. Are you even playing 5th edition? Everybody can get a cover save really easily. Sure, you can kill infantry out in the open but nearly any weapon can do that. Second, wounding on 2+ means you get 5/6 hits as wounds. Wounding 2+ with re-rolls means you wound 35/36 hits. I know which I'd prefer. I also prefer not allowing other Dark Eldar players, or IG command squads with medics, to take their FNP save. Against T6 you either wound on a poisoned 2+ or 3+ with re-rolls, which is damn close, with the slight edge going to necrotoxin. If you're shooting at a Wraithlord (T8), necrotoxin absolutely has the advantage, but you can just shoot at it with any other weapon in the army and the Wraithlord has a habit of dying.
I have more than enough poisoned weapons in my army, those kinds of attacks will never be in short supply. A little more isn't exactly appealing when there is an option that can fill a roll I don't have filled. If I want to wound mass infantry on 2+ and ignore 5+ armour, I won't spend the extra points and I'll just stick with monoscythe on a Razorwing, which also lets me ignore FNP in the same way as shatterfield. The big targets that necrotoxin would be more useful against still get their armour save, and are better dealt with using dark light weaponry or the high number of poisoned attacks that nearly any unit can provide.
As an afterthought, I almost forgot to mention pinning. I suppose if you run some Raiders with torment grenades right up to your target before you shoot, the pinning could be useful and that's a good application of the necrotoxin missiles. Other than that, pinning isn't reliable enough to be really considered, in my opinion. It's a nice bonus, but nothing to base a choice around. Also, a canny opponent is just as likely to go to ground, surviving a lot more shots.