Excellent research, spanner-weasel; thanks for sharing!
article confirms, some time must pass before the dead battery is charged (not exactly a "jump-start" situation), and--as the article says,
If you want a portable model, the Black & Decker is the only one worth a try. But be sure to keep it charged. Your best bet is to buy a set of booster cables at least 12 feet long and between 4 and 6 gauge. They don't need maintenance, and as long as you have access to a second vehicle, they can be used to jump-start any car.
I made up a charging cable myself; plug for 12-volt receptacle on the depleted-battery bike, and alligator clips on the wires to attach to a "donor" battery, from another motorcycle or available hot-batteried auto, etc. Would take some time to charge, unlike the 4-6 gauge jumper cables, but--more compact than the heavier wire set.
As to the on-board charging battery, your alarm backup battery is as good and idea as the purpose-built BD product, and . . . an actual SPARE battery wouldn't take up much more cube and tare than either product.
A more optimum solution, IMHO--kick-starter, and ignition circuitry running independent of the electrical storage (battery) circuit (e.g., Generation I CDI).
Again, thanks for the research, spanner-weasel!