Having never had the DIAD 3 clip (I started post DIAD 3), I've never known anything different.
Some others I work with still rock the 3 clip and won't use the 4 clip...
I find that there is a sweet spot on your belt with the 4 clip where the DIAD won't rock back and forth when you're walking. It works for me.
I fell out of the back of my package car yesterday, flat ass on the ground (no good story, just a super-clumsy move, I was totally fine). I fell on the ground in full view of a small private school office...that was embarrassing enough, but my 4 clip did not survive the fall and I had to carry the DIAD in like it was just another package.
Sweet!