Very.
A higher stagger limit but lower cleave/damage limit than lights.
They’re good at staggering maulers, bestigors and stormvermin at least; light 1 & 2 are better at staggering savages & monks oddly enough.
Not sure how I feel about moving the stab to heavy 1, I quite like push attack > light 2 > heavy 3/stab.
Heavy 2 could do with an AP headshot buff.
(It does maybe 2 - 3 more damage than a push attack/shielded poke)
The actual attack is reasonable but the recovery time feels dreadfully slow.