[iadP > K] is easier to time than [iadK, K]. jP is 1 frame faster so the timing on the initial hit is a bit easier, mostly. Link is still easy (though if you somehow got the right height you could just gatling it?) so if you're not confident in your iadK timing, it's a pretty decent substitute. jP IS a good 18 points weaker damage-wise than jK and takes off a bit more guardbar (GB-8 as compared to GB-7), though, so you are losing a bit of damage and generally there isn't a situation where you can do [iadP > K] where you can't do [iadK, K]. Or at least I haven't encountered any.
-edit-
iadP > K is pretty much as easy to hit 5H off of as iadK, K. You can do the jK really late anyhow (jP, jK is an 8 frame link anyhow) and the timing is pretty similar in the long run to [iadK, K]