"Opinions? "
I got my first Lee collet neck sizer maybe 22 years ago just to see what they were like. I soon had one for every one of my accurate cartridges and haven't used a conventional neck die since. Yeah, there's moving part and, yeah, it takes a bit of learning to use properly - it's not a simple "push the case in, pull the case out" like the others - but it's worth taking the time to learn to do it.
The collet's inside mandrel does three things for us:
* It minimizes the amount of neck working so cases last as long as possible.
* Done properly, it limits the sized necks for all of the possible 'bullet tension' that means anything.
* It insures the straightest possible finished necks so runout is minimimal.
The Dead Length seater screw plug is nothing but a fixed stop for the floating internal nose punch, seating pressure will take out any slack you may see when it's not under pressure and it will not move unless the user turns it. Used correctly, that seating die will eliminate any OAL variations due to press spring or sloppy operator technique.
Sounds like you got an object lesson that it's good to chamfer necks before seating even if you aren't using lead bullets. That crunched neck thing wasn't because of the collet die, it would have happened eventually no matter what sizer die you used.
Many jacketed bullets do have a tiny bulge at the heel.