I have 2 styles of input shafts on passenger side cv. Anybody explain why the 1 has a waist cut in it? I’m going to use 1 for the Hagen mod - seems the non waist is best - but why the waist anyway?
 Did some searching couldn’t find anything here.

First - I can't open those images so I have difficulty understanding your question.

Second - I don't understand how you can have "two styles of input shafts on passenger side CV" - what are you calling the input shaft?  If I assume the what you're calling the input shaft is the end of the axle that goes into the differential, I don't see how you can have more than one input shaft, unless you have more than one passenger side CV axle.

I have a few of these axles that came as spares with the rig - hopefully the pics will be viewable now

The axles I have all look like the first or "non-waisted" version - I can't tell you why the other one is the way it is, but like you, I would think the non-waisted one is preferable.