We've got three of the Tube Tech multi-band units here. They get used for mastering, and not much else.
As for Fletcher's suggestion; ADR used to make a box in the 1980's which you used with their 'Gemini' stereo compressors (or anything else which took your fancy) to do multi-band.
It was used when we mixed 'Brotherhood' by New Order... -that's the thing I remember it definitely being used on... 'Bizarre Love Triangle' is one tune that I remember it being used on, for certain.
Looking at a spectrum analyser, you can SEE how it 'tames' the sound (which was pretty harsh, 'attack-y' and aggressive... well, this was the 1980's, after all!) -I'm not sure that I'd rush to try one for instruments, but if I had a particular problem of something 'popping-out' in a particular part of the spectrum, then I might call for one, but these days I tend to think that if you've got that much of a problem with a sound during recording, you shouldn't be recording that sound...
This sort of tool gets used by me when it's 'too late' and something which has already been mixed needs to be 'massaged' a little.
Keith