I didn't mind it. I think they should've stuck with "Believe it" in part 2 instead of changing it to "ya know".....the believe it was a more impactful trademark phrase to me....
Imagine if he said to his mom, "I've wanted to meet you for so long...believe it"......or Kushina saying, "wrong...believe it".....
It's more unique IMO and would've been something that was just between them.
Everybody and their momma says "ya know".