I think it’s 10% more explosion speed. so it multiplies, at most, damage by 1.1^drf . It goes at max to +9.16% application rage ham, 8.77% for fury HM and rage rocket, 6.7% for fury LM. Again, that only works when the sig of the target is big enough to not be limiting tthe DPS already.
Now, using TWO T2 intead of one T2+one polybolos makes you gain 4.05% DPS. even against the fast BS, using two polybolos with CN tops (and no other apply mod) makes you gain only 5.25% DPS over two T2 , and using rage torps it goes to +5.52% DPS. using only 1 poly +1 T2 instead of 2 T2 gets a +3.5%increase.
So If you have no apply mod, and are far below the sig of the target, then it can become usefull to apply. but really in that case, switch to another weapon system. or bring some apply mod. a rigor T2 gets you +25% apply IIRC. And is always effective(sig can counter effect speed, but speed does not counteract sig).
TLDR : polybolos can give you up to 3.5% more DPS if you have very bad application, but in most cases using a painter/rigor, or switching ammo, is much better.