I purchased a 21 st Century hand prime, and it had a second generation Auto Prime tray.
While I like my 21st century tool, the second generation tray has all sorts of feeding issues. Lee must have gotten tired of all the complaints, and that variation is gone and now they are using the current Auto prime feeding system. You can tell, by virtue of the second generation tray, that Lee had to change the feeding system because primers were igniting and setting off the primers in the tray. The second generation tray keeps any flame spray above the rest of the primers. Because all settlements are arbitrated, or are sealed, we will not hear of these things from the people who were injured, but, you can tell just by the design changes in the tools, that the manufacturer is making those changes to reduce their liability. As they say, where there is smoke, there is fire.
http://www.xxicsi.com/auto-feed-ss-priming-tool-for-the-lee--new-auto-prime-tray.html
But, I happen to have old Lee Auto Prime trays sitting around and when the tray on my 21st Century finally breaks, as it will, I will install new old stock Auto Prime trays.
I do like my 21st century unit, I can use all my old Lee Auto Prime shell holders, over the decades I have lots of them, and worst of all, duplicates! I have bought enough shell holders by memory, and found once the new one came in, I already had one! Argh! The old Lee Auto Prime, I don't recommend as the zinc die cast tool will break. I broke maybe ten handles, they just break in time, and in time the shell holder cracks the top of the tool body. The 21 st Century tool is all aluminum and so far, except for the stupid tray, works well.
The outrage about accuracy sales hype about primers, priming tools, is spot on. Primers are in the "noise" level when it comes to accuracy. I do believe they make a difference, but the affects are much less than the barrel, the bullet, and good bedding. In my experience, these have been primary contributors. After shooter inaccuracy. Then comes cases, powders, primers. The affect of primers is hard to quantify because primers vary so much, within the lot. Primer mix varies from lot to lot, because the percentage and quality of the components in the mix, vary from lot to lot. I do believe that if a primer lot does not provide a consistent spark that will make a difference on target. However, without test equipment to measure the material ejection, flame temperature, we in the public, can't measure those things and make any real correlations about their affect on pressure or combustion. Primers are subtle.
I would say, if anyone is having problems setting their primers on a Dillion progressive, call Dillion. I had issues, they sent me enough parts that eventually, everything worked out. Dillion has a real "NO BS" warranty that they stand behind. Kudo's to Dillion.