Why does Nosler advise special caution when loading the E Tip? What is the difference in penetration/expansion between the E Tip and the Ballistic Tip in real practice? Thanks

The E-tip is seated in a soft copper bullet body and the tip is a newer design plastic.
The original Ballistic Tipped bullets were of a different plastic that did in fact melt at longer distances due to air friction which affected accuracy to a degree and degraded bullet performance when the target was struck.
The E-tip bullet plastic is harder and if the bullet seater is shoving directly on the tip,could misshape the nose of the bullet jacket affecting accuracy.

Nosler's E-Tips are monometal bullets like the Barnes TTSX. That makes them longer and harder than a typical lead-cored bullet of the same weight and therefore likely to generate higher pressures from the same load.

I've never used the E-Tips, but if they perform like the similar monometal TTSX bullets they will penetrate better and retain weight better than the Ballistic Tip. The TTSX is by far my favorite game bullet, very effective!