I would say rather useless...
Against a big armoured warship the damage of 4D + 4[added dice] + 4[added Effect] ≈ 14 + 4 + 4 ≈ 22. After armour 7 damage per shot and 6 shots, so average damage 42, less damage than the corresponding fusion bay, at shorter range.
We could use it to produce large amounts of crits against very large ships, but again at short (well, medium) range.
We could of course easily incinerate a Free Trader, but any 500 dT bay should do that...