Manichean Christianity?

Manichaean Christianity is a spiritual stream-  as is Rosicrucian Christianity. The Manichaean stream continued on in Grail Christianity.

Was Mani a Christian?

Quoting a page:

"Notwithstanding the calumnies heaped on Manes, Dr. Lardner has shown that he was, in the best and strictest acceptation of the term, a sincere Christian, and has adduced many passages from his writings equally honourable to his understanding and to his heart."

"One has to read St. Augustine's anti-Manichæan disputes to realize the extreme ingenuity with which scripture texts were collected and interpreted. Though Mani called himself the Paraclete he claimed no divinity but with show of humility styled himself "Apostle of Jesus Christ by the providence of God the Father"; a designation which is obviously adapted from the heading of the Pauline Epistles. Mani, however, was the Apostle of Jesus Christ, i.e. the messenger of Christ's promise, In A.D. 1000 the Arab historian Al-Beruni wrote: "The majority of the Eastern Turks, the inhabitants of China and Tibet, and a number in India belong to the religion of Mani".

The Syrian inscription reads: "Mani, Apostle of Jesus Christ"- Rock Crystal,  Bibliothèque Nationale, Paris

Most of what you read on Manichaeism was written by its enemies and not to be trusted for that reason. The religion was subject to one of the most massive persecutions history has seen. The Manichaeans themselves were a non-violent people following the principles of the "Sermon on the Mount". It is true that some of the later sects did drift into the Lucifer/Gnosis notions.

Though the Cathars were seen as a later form of Manichaeism there is no direct link.

Christianity became the culmination of all the ancient mysteries and religions. It is not surprising then, that one finds elements of Buddhism, Zorastrianism, Empedocles and Pythagoras in Mani's teachings.

“As water will be added to water and becomes much water, so were the ancient books added to my writings and became a great wisdom the like of which was not proclaimed (hitherto) in all ancient generations.”

(Kephalaia, chap. 154)