Transformer provides the same low frequency distortion that audio transformers produce.
It gives you a rough approximation of an analog sounding mi when used on the master bus. It allows you to do this without getting signal degradation that DA-AD converters produce. Its effect is deliberately subtle and may not be audible on undersized speakers or low quality headphones.
The plugin uses a low pass filter followed by a cubic function generating pure third harmonic distortion. This is then mixed with the original signal. The LF Distortion Bandwidth setting is the -3dB point of the low pass filter. The LPF also serves as an anti-alias filter. Worst case alias product (with 0dBFS input at just over fs/6, at maximum bandwidth setting) is at -120dBFS.
Third harmonic distortion is around 3% at 0dBFS at frequencies below the LPF cutoff. Distortion decreases with the cube of the signal amplitude, so for every 6dB reduction in signal level the distortion is reduced by 18dB. There's around 1dB dynamic range compression at 0dBFS at low frequencies, and the plugin provides about 0.5dB of LF makeup gain. It needs to be driven fairly hard (loud peaks at -6dBFS or more) for the most noticeable results.
This plug-in does not affect the CPU as much and can be handled by any Linux based computer.