I liked that you get two plug-ins: the ML1 mastering limiter that works great when you don't need multi-band capability and the four frequency band ML4. Both use the same limiter algorithm, a flexible brick wall look-ahead design and multiple stages of limiting for exacting peak processing.

I found the ML1 perfect to solve dynamic problems on individual tracks within my mixes--tracks that were recorded badly and varied greatly in level. I had a wah-wah guitar track that never really settled (in level) into the track like I wanted. Short of riding the level for the entire song (tedium no mixer likes), the ML1 controlled it perfectly with minimal added distortion.

The ML4 can change the overall spectral balance of an entire mix or any individual stereo track. It's perfect for tweaking a finished stereo mix where perhaps there is not enough lead vocal or the bass is overly loud. The ML4 has a 4-band gate, expander (upwards or downwards), and compressor. Each frequency band's gate, expander, and compressor can act separately or be linked together. These four bands have very sharp and precise 24 dB/octave crossover filters making it easy to pick out predominate vocal frequencies and boost only those (for the mix with not enough vocal track) without affecting frequencies above and below.

Other cool features that put the ML4000 in my favorites plug-in list are: Style Modes--Clean, Dynamic, Crush, Soft, Loud, and Smart--where a secondary detector defines the ML's overall sonic style, I.e. you are not stuck with a single overall sound no matter how you set it; both the Knee and Mode controls allow the ML limiter to respond anywhere from transparent to aggressive; and the three filter crossover points are graphically adjustable showing a dynamic plot of the input, output and sum of the dynamic actions of the gate, expander and compressor.