Have been shooting a Hornet since the '70's in several rifles. It is my choice for varmiting around livestock, since it does not spook them as bad as the heavier cartidges. The farmers get a bit irate when their cows slam them into the fence when a shot is fired. Have used nickel and non-nickel brass and see very little difference in case life. Never seen any flake off, and also never seen any detrimental affect on dies. If you like them, use them.
Also owned a K Hornet for a while. The differences in velocity were minimal, 100 ft/sec at most, and unlike another poster, I saw much reduce case life in the K Hornet, even with annealing after fire forming. All in all, it was not worth it. I traded my K Hornet at a gun show to get it off my hands.
Fav powder for the Hornet is AA1680, hands down. Using a load that is slightly over max recommended by Accurate when it first brought out 1680, my Handi-Rifle SB1 shoots Sierra 45 gr. Hornets into 5/8-3/4" groups as long as I care to pull the trigger. I did have the trigger worked on by a smithy, however, as it was stiff as a board from NEF. I use an COAL of 1.775", CCI450 primers and Rem brass.
I have eliminated 138 groundhogs this summer with the Hornet so far, and only one miss, in high winds. I will never be without a Hornet in my arsenal.