Seems to me the 21st Century, Frankford Arsenal, Darrel Hollands add on for the RCBS bench primer, and the K&M unit will all allow for precise seating depths. Frankford Arsenal being the for budget minded
I can only speak for Holland's perfect primer add on for the RCBS which is not exactly cheap @ $170 plus the cost of the RCBS unit or $320 complete but I can dial in seating depth to .0005 if I want to. I don't bother and just seat everything to .003 below flush, honestly never tried any other setting. Maybe I should but .003 seems to work well. It is also easy on my hands, 50 years of weight lifting and twisting wrenches took a toll. I have been using it for about three years now and would never go back to a hand unit
I can only speak for Holland's perfect primer add on for the RCBS which is not exactly cheap @ $170 plus the cost of the RCBS unit or $320 complete but I can dial in seating depth to .0005 if I want to. I don't bother and just seat everything to .003 below flush, honestly never tried any other setting. Maybe I should but .003 seems to work well. It is also easy on my hands, 50 years of weight lifting and twisting wrenches took a toll. I have been using it for about three years now and would never go back to a hand unit