Yeah. Big, huge differences. My husband uses what I call “brand x” version - New King James, I think. It drives me crazy when we use it in devotions. He says he can’t understand KJV. I’m not buying it since he has a PhD in Physics. He can understand.
I can’t remember the study now, but the readability of the KJV was on the 4th or 5th grade reading level and the NIV was rated college level!
Started my kids on it in kindergarten and they grew up with it. They might not have understood the doctrine, but they were sure about to read it!