Interesting - never heard of Frenzel before. But I've just googled it + testing it out and it seems like a better alternative! Thanks!
remember that Frenzel is mostly used by free divers, as you have to hold your breath while doing it, usually with the mouth closed. so you have to remove the reg from your mouth...
The Marcante-Odaglia is an Italian variant, developed specifically for scuba divers using the ARO (a closed-circuit pure oxygen rebreather, which was the most popular scuba system here up to the seventies). With Marcante-Odaglia you do just a "partial" Frenzel, not involving the mouth and leaving the glottis open, so you can continue breathing normally from your reg while equalizing, You still need to close your nose, indeed.
Most scuba divers who claim to be using Frenzel, are in reality using Marcante-Odaglia. On the other side, free divers who are using the real, more powerful Frenzel manouvre, have problems using it when scuba diving, as the pure Frenzel require to use also the tongue, closing your mouth.
There is a third method, developed in France, the one I use mostly, called BTV. This does not require to close your nose, you simply use specific muscles inside your skull, which open the eustachian tubes. It is not easy to get control of these muscles, but as you learn doing this, equalizing will never be a problem, as, if you want, you can keep the tubes open indefinitely.
And, for completing the panorama on equalizing techniques, there is a fourth one, called Toynbee, which is done closing the nose and swallowing. This is particularly effective for solving a reverse block, which happens when air is trapped in the medium ear and does not come out through the Eustachian tube while ascending.
Toynbee stays in between Frenzel and Marcante-Odaglia, as swallowing you need to close your glottis, but you can keep the reg in your mouth, suspending breathing while swallowing.