Well a scatter serpent is set up like this
What this gives you i 7 str6 shot that are twin linked and up to 7 str 7 shots from the shield. The shield is also twinlinked because of the scatterlaser. It also ignores cover and causes pinning. perfect for taking out pathfinders,rangers, ratlings and scouts. Units that rely on cover.
At anti air the scatter serpent works out better at killing aircraft then any other setup.
For anti infantry lets day a 10 man imperial guard unit. Lets say you hit with your blast missile you get 3 hits. 2 will wound and lets say another two from the cannon. you have killed four and caused a pinning check.
for the scatter serpent you have 4 hits and 4 wounds and 3 dead. then the cannon another 2 and the shield and we say it got 4 hits including the +1 so that would be four hits, four wounds , 3 dead. all together 8 with a moral and pinning check. against vehicles lets say a Chimera. missile 1 hits and then 50/50 to glance/pen and more then likely no glances with the cannon. scatter serpent. with str6, 6 hits. 1 glance. shield 4 hits and a 66% chance of causing glancing and pens. and it ignores cover.
God that was a lot of math.
6th Edition. 7th Edition