I tried the Gliss demo and it is a really nice EQ with filters and the ability to adjust gain based on program material. It would likely work well in a lot of situations if you need a really good EQ with db sensing and auto gain adjust.
 
It doesn't have the functions that Pro-MB has with regard to compression limiting and expansion.Not having personally tried this plug-in yet I am in no position to comment on what it can do as of yet.
 
From my vantage point I can see that it would probably be very beneficial in a case where maybe you want to add some compression to a narrow frequency band which is basically what an MB does only Pro-MB goes a few steps further in side chaining options and adds more flexibility in the types of compression added and mostly in its ability to get to the heart of the matter with great controls a useful GUI.Fab Filter seems to be great at intuitive layouts and making maximum use of controls.
 
You don't need to go through various screens in order to get the job done.It looked as if it has presets if you want to use them to get started on something and tweak later, but It seems to be limited to an octave. You can slide the octave and you have pretty good control in that range, but there are times when you might want to compress only a small part of an octave,maybe just work with the tink of a cymbal in a narrow range,say right at the point of contact and then discard the tail, or one small segment of a guitar part.Compression would do the trick in some cases but not always. Now you can adjust EQ, exciter,compression,limiting and side chain all in a simple GUI and in one Plug.
 
 
 
 
 
 
 

Pro-MB's bands are fully adjustable. Unlike classic mult-band compressors, they don't even need to overlap. 

As for GlissEQ, it isn't really a dynamic EQ in the classic sense. The dynamics control just alters the attack time before the filter kicks in. The closest thing I know of out there is Meldaproduction's MDynamicEQ. It's actually quite similar to Pro-MB in how it works, although the UI is radically different.
 

For non-polyphonic tracks such as bass and vocals, you often don't need a multi-band at all, just a broadband compressor that offers a filtered sidechain. Pro-C is my usual de-esser, for example, although Pro-MB also does a great job as a de-esser.
 
Where the multi-band is most useful is when there is a lot of variance in certain frequency bands, such as parts of a song where there's too much happening in the low mids but conventional EQing would make it too thin in other parts.  Or a vocal whose timbre changes greatly from note to note and phrase to phrase, typically due to the singer not being consistent with distance and angle from the microphone.
 
Another potential scenario would be enhancing transients using expansion, but I haven't had a chance to try that yet.
 

bitflipper - I've noted your acknowledgement Pro-MB won't be a bread and butter tool. You have some specific uses you're thinking you'll apply it to.
 
For others, I'm reiterating that I think for a bread and butter tool, Alloy 2 is pretty fantastic.  It has multi-band compression as just one of its swiss-army-knife capabilities.  The multi-band in there can be quite surgical, but admittedly not to the ridiculous degree Pro-MB can.  From my experience, Alloy 2 is super easy to comprehend, with a logical workflow and interface.  Unlike some of the software additions I've made over the years where I've been impressed with the addition and liked it for what it did, with Alloy 2 I felt I had acquired a game changer in my capabilities to get some of the refinements I'm looking for in the mix.

You've sold me, Roger. As soon as my lottery dividend checks start to arrive I'll be adding Alloy to my shopping list! (Yes, I'm an optimist. I haven't actually bought a lottery ticket in years, so mathematically the odds are pretty low.)

I've got my Alloy 2 at KVR for $90, just browsed, none for sale now. You may have some extra balance on the day :)

bitflipper -
 
I haven't been mentioning Alloy 2 as an additional buy that would require lottery earnings.  I've been suggesting for some (not for you perhaps), that it would be a wiser spend for less cash out of pocket. 
lessee:
 
 
- Pro-MB - lists at 229 right?  You can use it for non bread and butter purposes. Kind of a nice to have.
 
- Or one could spend $199 for Alloy 2 (at list).  It is applicable for bread and butter purposes and can make a wider range of stuff sound great.
 
More bang for the buck as they say.
 
Unless you're enamored by FabFilter and committed to Pro-MB for non bread and butter pursuits.
 
 

bitflipper
This triggered a minor epiphany. It occurred to me that over the years the ultimate usefulness of a plugin has been inversely proportional to the ease with which it was learned.
 

Sorry bit, I just can't resist reminding you,
 
Are you sorry you passed on the Waves one Knob deal now?
 
All kidding aside I've had that same epiphany myself on many occasions.

I'm waiting for them to bundle the One Knob series with their upcoming One Note Synthesizer. But I'm going to beat them to the punch with my fixed-Q Single-band Equalizer.