[exray]

2. I'm drawn to the units that have both voltage and ampere meters, but how important is an amp meter?

An ammeter is a necessary part of the setup. Voltmeter isn't. The goal using a Variac is to be able to bring the voltage up slowly while WATCHING for something to go wrong. Without an ammeter your first and only indication will be smoke or sparks - exactly what you would have hoped to avoid in the first place. You can always use an ammeter externally, however its convenient to have one as part of the package.

As for size rating, you have to consider what you'll be using it for. If you want to work on old TVs, for instance, you have to consider the wattage or current rating which may be several times higher than what is needed for ordinary table radios.

-Bill