Bill Bonney recently made a blog post about these -- including a how-to on replacing the shaft.
I just checked the runout on a couple of these and found no more than .004"
Please note that the prop should go on first so that it fits down over the unthreaded shoulder of the shaft. This provides a slop-free fit on the shaft. The spacer goes on top of the prop, followed by the cap nut.
Alan and I were talking this over today, and realized that the spacers are not needed at all. The prop nuts have enough internal depth to seat on the prop directly without bottoming out on the top of the shaft (NOTE: if your prop hubs are thinner than the 6.5mm APCs then you may need the spacer). One less part to fiddle with and a little less rotating weight!