I've used the Hornady concentricity tool (one from P&D) on calibers ranging from 223 to 300wsm...so far I have yet to see more than .002 total run-out...and rarely do I see that much. The norm is about .0005. So, as long as your dies and processes are good, it seems that this tool is just for the occasional shoulder check. I've also compared run-out on bullets that are sized with full-length dies, lee collet dies and bullets that are crimped with Lee Factory crimps...again, throughout all of these procedures, no more than a maximum of .002 run-out....and Hornady says that anything under about .003 is good.
Bottom line, it's fun to own the tool....but, for me, I don't see how it adds value...least, not yet.
Now, if I could only find the ideal solution for avoiding stuck 223 cases! Seems it's quite an art to get just the right amount of lube....I'm using RCBS wax. I also think that it might be differences in the brass...some brands seem to be softer than others.