That is what most people think about those devises, but they actually only use the vacuum and compression to operate a diaphram and piston type valve to suck in fresh air from the slots in the unit, so the tyre is inflated with normal air,
But they are as slow as 12 volt compressors, except they don't overheat and burn out, so can be used for large tyres... the 4X4 lot used to love them, but nowadays they tend to use an air con compressor as an engine driven air compressor and a tank for onboard air to operate the air diff lock, suspension air bags and adjust tyre pressures.