I bought two neck sizers and never will buy another. The redding competition Bushing neck sizer is ok since it supports the brass and keeps it centered. But the RCBS just makes things worse. I can get by with neck sizing a once fired formed piece of brass without much trouble, but more than that, the neck gets out of round easily. I do Partial Full length. But doing that, can be hit or miss. You really need to measure how your shoulder to make sure your not bumping it back, so setting up a partial full length and doing it consistently can be tough.

So for the sake of simplicity I mostly full length size as long as I am happy with my groups. And I am.