I personally have no idea what M-O is. I google translated the Italian article and it does sound like Frenzel. But reading
@Angelo Farina's description, it does sound like a form of VTO.
I also am not sure you can keep the vocal fold open when doing Frenzel or VTO, when I lift back of my tongue, mine closes automatically and I suspect this is a reflex for protecting the airways during eating or swallowing. Same goes even for Toynbee, the fold will close momentarily.
@daviesrye my take on humming exercise is that while humming and trying to lift the back of your tongue, you are trying to find the spot where ET is opened. When ET is open, you will hear it because of hum and once you learn the correct spot, there is no need for humming. But again, there is no right or wrong on this, if it helps by no means do it. VTO is not as strong as valsalva or Frenzel, so, you have to do it more frequently, this is expected.
Marcante-Odaglia is "Frenzel for scuba divers", while pure Frenzel is employed mostly by free divers. From outside, the main difference is that a free diver has the mouth closed, while the scuba diver has a reg in it.
For most people there is no practical difference, and in fact most of people (and instructors) think that Marcante-Odaglia and Frenzel are substantially the same.
Outside Italy, the name Marcante-Odaglia is not widely known.
And outside Italy, scuba divers usually do not use Frenzel (or, more properly, Marcante-Odaglia), as PADI-like instructors typically only teach Valsalva (when the whole OW course lasts 3 days, there is no time for exploring many different equalization methods).
Frenzel is taught in (deep) free diving course, and in this case, it is correct to call it Frenzel, as it is performed with no regulator in mouth.
For more details in what happens inside our skull while performing Frenzel and M-O, look at the two last figures I posted. But be aware that these figures represent respectively a "pure Frenzel" (where the soft palate is left "neutral", open) and a "pure Marcante-Odaglia" (where the epiglottis is open, so you can breath while equalizing). Many divers perform both these actions simultaneously, so they raise the soft palate, closing the passage between mouth and nose, and then they also close the epiglottis and push the tongue back, so the two actions are summed, resulting in a much higher pressure and more powerful equalization. And this combined action, including the closure of both soft palate and epiglottis, and exerting pressure both with the tensor palati and tongue, is usually called "Frenzel" by people who are not aware of the difference between these two very similar equalization methods.
BOTH M-O and Frenzel ARE WITH
PINCHED NOSTRILS;
Instead BTV (VTO in English translation) does not require to pinch the nose, nor to perform any strange contraption of tongue, soft palate, or epiglottis, swallowing, yawning - NOTHING! If you need to do any of these actions, that is NOT pure BTV...
BTV simply and directly opens the tubes. As said, I use BTV since when I was a child, I can open my tubes whenever I want, and as long as I want, even while breathing or while speaking, and with the tubes open I hear my voce through them, the sound is quite funny...However, even if not speaking or humming, when the tubes are open the sound coming form outside through the nostrils is quite evident, so there is no need of making any sound for understanding when the tubes are open. Juts the air flow through the nose makes a lot of noise when the tubes are open!
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