I have the Sinclair press and I like it a lot. First off, there is NO fussing and minimal setup - grab it, quick-set the height to a custom fit to any caliber, and go! It is very sensitive to presure variances - that is you can really feel the difference in seating pressure, which is important for paper punching, especially.
But, I used a small wood disc made of 1/2" plywood in the palm of my hand for years before Santa gave me a press for Christmas one year.
I guess I would say it is a
nice to have piece of equipment, not critical to success, however. Kinda like air-driven wrenches, or self-propelled lawnmowers, and flush toilets...
P.