Just make sure the door lock is on the INSIDE!
The pins made small scratches & a little peening the first time I used them. By the 5th to 10th batch of brass the shine really comes out. It depends on how much to tumble per load & how long you let it run.If the steel pins are peening your cases, your cases have been weakened by reloading, not by cleaning with the steel pins.
Cases that are in good condition are not affected by the steel pins if you don't over process them.
If your cases are peened after you wet clean them then the brass has been thinned by shooting, sizing and reloading.
I'll qualify my statement by saying this is both my experience and my opinion.