Q: The Maulerfiend model has a pair of magma cutters. Does this
mean that if it hits with at least one Attack in the Fight sub-phase
it gets to make one additional Attack with each magma cutter and
if it hits with all of its Attacks, it instead makes two additional
Attacks with each of its magma cutters? (p68)
A: No. The Magma Cutters rule covers the effects of both
the Maulerfiend’s magma cutters, which are treated as a
single weapon. They are also treated as a single weapon for
the purposes of Weapon Destroyed results.

I'm glad I was right about this one too.