This is very versatile plugin. It can be very subtle, but you can crank it up and get really cool saturated "analoguesque" tone.
I use this plugin to tighten up my whole mix, it works very good at this.
More fun you can get by flipping the "mic" switch - you can hear some really cool colorisation effect, some kind of a good old vintage preamp's sound.
My top rated plugin, must have!