Metallizer paints

I can't answer specificly as to difference between acrylics, enamels, and these,  but I will presume it is the formulation of the paint itself.

Yes the MM Metalizers are supposed to be airbrushed, although they can be handbrushed in small areas. Over bigger areas handbrushing does not look good at all...

The sealer is applied as a final coat to prevent the long term changing or tarnishing of the metalizers that will occur thru handling, humidity, etc. But that sealing coat looks like just that and does not give that bare real metal look that the unsealed Metalizers have.

Yes, buffing the buffable ones out gives them more sheen/shine.

Yes, I think that they are worth buying and using.

Testor's Metalizers are lacquer paints, they also have their own thinner for cleaning your airbrush out, though other products may work as well. They're not very tough finishes, I've never been able to mask over them, and it'll come off on your hands well after they're dried. I like the buffable versions, as it gives you a choice in final sheen for the finish (buff some areas, and leave some areas alone for variety). They work straight from the bottle in the airbrush with no thinning needed. A lot of folks like the Alclad, but I could never spend that much on one bottle, so Testor's is my choice.

Glenn

Masking is easily done using parafilm M, or wet newspaper strips laid in place