Mauler Fiends & Spawn - Sleeper hits?

So having come fresh from a bunch of good games i've decided to shed some attention on a few underrated unit in the chaos book that i've been using

Chaos Spawn and the Maulerfiend

Both have a 12" move. Both can fleet and completly ignore cover. Had 4 good games yesterday and both these units were in combat turn 2 at the very latest, even on longways table deployment.

The Spawn get rage and random attacks. Meaning on the charge they get a minimum of 3 attacks each, up to a maximum of 8. Combine that with S5, the potential to count as poisoned, so re-rolling failed to wound, fearless and with the right marks T6 with 3 wounds these guys don't go away in a hurry. Marines need 6's to wound. These guys cn either tarpit the hell out of a unit (held up a 20 man Chaos Marine squad for 6 full turns, held up a Necron Destroyer Lord and 3 wraiths for 4 full turns) or smash in and crush them.  Nothing can ID them in shooting. They took fire from 2 Contemptors, a squad of long fangs AND 3 land speeders in a single round of shooting, with no cover and only lost 2. They then charged said land speeders and smashed 2 of them in one round. A unit of 5 with Mark of Nurgle is only 180 points. And thats 15 T6 wounds. With 15-40 attacks on the charge.

Backing up the fast movers is a Maulerfiend. I learnt - people are terrifyed of this thing. People were redeploying deepstrikers and everything, using all heavy weapons on them. And thanks to their 5+ save and my intense luck, he rarely got scratched. And when he hits....boy does he hit. 4 S10 AP2 attacks on the charge, with the potential for another 2 melta hits. I take the magma cutters over the whips because;

a) he needs a bunch of attacks to be effective and
b) the biggest threat is grenades. Where the enemy only gets 1 attack anyway.

Except in places where I whiffed on my dice (seriously...2 turns, 7 attacks in total, not 1 4+ to hit), this guy smashed his way through everything I put in front of him. If its a vehicle and it hasn't moved, it is dead. Regardless of armour values. For 120pts you can't go wrong.

Working together presents a threat to the enemy. They're so fast, they need to be targetted. Combine them with a unit of bikers moving fast and making a threat of itself and the enemy has to target them or be killed, giving you a shield to move up slower units in rhinos or one foot.

Definently 2 of my favourite units in the dex. The obvious things (the dragon, the Apostle) all do very well, but theres just something about these guys that stands out

If 2 are good, 4 must be better right?

4 Nurgle Spawn for my chaos army. 2 did pretty well, so i figured 4 would have to be better