I have both.
Hand priming tools are nice as you are not tied to the bench and can watch the tv, kids, whatever during the mindless task. Having the primers held on basically the same plane and potentially right next to priming operation doesn't strike me as the safest design, but ignition is rare as understand it.
Bench priming tools give great feel and probably more consistent results. If you mounted it to a block it would be portable in the sense you could clamp it wherever. Loading tubes is an extra step, however in the unlikely event of ignition the RCBS has the tube a good distance from the priming operation.
Before my progressive I used a Lee hand priming tool for pistol and bench mounted RCBS for rifle. If I had to pick one, bench mounted, but handheld are very affordable.
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