Racinbob,
RCBS sells the square tray upgrade for the original hand primer. You don't get the universal shell holder, but you do get a larger tray that is easier to load, and feeds better from the corner than round trays feed. Pretty cheap IIRC.
I started with a Lee hand primer, but the thumb action was giving me problems when I would prime more than a hundred or so at a time.
I switched to the RCBS Universal, and am glad I did. I kept the Lee for small primers for a while, since I don't load as much of them as I do large primers. Then my wife bought me a second Universal, and now I keep one set up for each size. The nice thing about the two tools is their trays are universal, so I can load two trays with 200 large primers each, then go sit in my easy chair and prime cases for a while. My thumb would have fallen off If I tried 400 in a sitting with the Lee. I also like that the universal tray slips out of the handle so that they can be stored more easily and compactly. Laying the tray flat on the table makes it easier to load too.
Since I have a co-ax press that does not use shell holders, having a hand primer that also doesn't use them helps a lot.
Andy