"Their 4210A is listed as "positive ground" which has me befuddled."
Obviously, you've never worked on an old VW Beetle.(G)
Also "positive ground" and if you tried to jump start one "the" universal way, you wound up blowing up two electrical
Could be that some of the electronic components have live electrical
connections, on the positive side, to an external heat sink attached to the case, or something equally simple. Or perhaps, that's a special model designed to be compatible with older VW Beetles.(G)