Amazing Isometrics- how it works

As in title, I would be very pleased if someone (vet or no-vet) could explain how exactly this exercise works.
That’s the original thread, where I also posted a reply. Amazing Isometrics - expand gain potential and cut down PE duration
Maybe this works on smooth muscle maybe on tendons/ligaments maybe on tunica, but on which one?
Bird2 claims he got improved PE gains from this. Maybe it’s just better EQ from exercising the BC muscle?
It’s good to add that I’m using it and haven’t seen lost of gains. I know the rules “Everyone’s body is different.” “PE is a marathon.”, but maybe it simply doesn’t work? Maybe Bird and everyone who does/did it has gained only from jelqs/stretches/other?
Also, I think the final question: if it works, what’s the indicators that I’m doing it all right? There are PI’s for PE in general advise, how not to injure yourself for EG. During clamping, why shouldn’t be the PI for this exercise?

Best wishes and happy gaining.

Sorry, forgot to add a “?” at the end of title.