It's multiplicative, but only on the the critical strike bonus. So your crit is actually (1 + 1*1.3) so you get the same effect as if it were a 30% additive increase.
It's multiplicative, but only on the the critical strike bonus. So your crit is actually (1 + 1*1.3) so you get the same effect as if it were a 30% additive increase.