The cheap, lightweight unit is essentially a light dimmer, permanently set at 50%. It works for things that are heating devices; irons, hair dryers, coffee makers, etc., and of course, incandescent lamps. It chops up the 220 volt coming in, then the heating element or filament averages that to something equivalent to 110 volts. DO NOT use these for anything electronic! You will probably be very unhappy if you do.
The big, heavy, and pricey unit is an honest-to-god transformer. It will keep your electronics happy, even if it is a pain to carry around.
Hope this is useful.