Is it true that congregational takbeer with one voice on eid is a matter of respected difference of opinion? They claim imam ash-shafi‘i mentioned its legitimicy. And that the malikis have differences here and quoted the hashiyah of ad dasuqi.

No, and the two things are not the same question. Raising the takbeer aloud, each person on his own, is the sunnah, while saying it in unison as one voice is what Imam Ibn Baz and Shaykh Ibn Uthaymin called an innovation. The text they quote from Imam ash-Shafi'i says that people should say the takbeer in groups and individually, which is not a statement about one voice.