"Thus the one you are loading is not in direct contact with the rest of the primers."
I haven't used the XR but the seating primers in my old AutoPrimes are not in direct contact during priming, it's physically impossible to do that!
I bought two of the very inexpensive AutoPrimes at once about 1990 because I'd heard the whining about breaking handles and wanted a spare. Set one up for small, one for large and both are still working fine. I do lube the wear points on the toggle links. And I stop to find out why a primer isn't entering normally; the Tim Taylor method of using "more power" to solve a problem seems out of place on small tools. ??
I've always put as many primers in the trays as I wished and have used thousands of Federal primers safely too. (I know why Lee suggests we don't do that and it's irrelivant to me because my working method prevents the potential problems.)