FWIW, to help answer your question Jaakko, I use mine 25% of the time on lows only, 74% of the time with lows and highs, and 1% with all three engaged, when something is a real mess.
Having said that, a simple +0.5 gain in the mid section can sometimes bring a vocal out like little else.
Mainly I use it as a 'clever' shelf eq. If I want to cut the low end then using the MLA-3 you can get the cut you want, but you get tightness/punch for 'free' into the bargain.
Certainly be interested to see what you came up with Jaakko!