Along with the previous Shatter Driver benefits, the Heavy variant now has an immense DPS increase which can greatly help the destruction of heavily armored foes as a Heavy variant on level II is already worth more than 2 level III Normal variants.
It also has a shield bypass bonus, it is not as helpful as the shields will most likely fall from 2 shots of the Heavy variant it still helps do more direct armor damage if the opponent is running away and is hit rarely by your weapons. This buff also goes well with the Siege Casing special as an even heavier support bonus.
Along with the previous drawbacks of the Shatter Driver, the Heavy variant is replaced by the Xeno Shatter Driver quite fast as the Xeno variant is a limitless blueprint. Due to the next drawback..
The Heavy variant is a reuseable item. Which gives you a limited amount to equip on your ships. This is bad if you want to use this on many different types of fleets as they are both very expensive and limited making it even more limited in combat.
It is also Xeno Division Hulls only, which limits the amount of options that it has in Fleet vs. Fleet combat.