There is a lot of great primary source material cited. Unitarians of that era believed in something that evangelicals of today could only regard as a cult like heresy. But they were far more biblical and theistic than the UUs of today.
From Jared Sparks' Unitarian miscellany and Christian monitor, circa 1821:
Unitarians believe, that Jesus Christ was a messenger commissioned from heaven to make a revelation, and communicate the will of God to men. They all agree, that he was not God; that he was a distinct being from the Father, and subordinate to him; and that he received from the Father all his power, wisdom, and knowledge. (p. 13)
Although unitarians do not believe Christ to be God, because they think such a doctrine at variance with reason and scripture, yet they believe him to have been authorized and empowered to make a divine revelation to the world. We believe in the divinity of his mission, but not of his person. We consider all he has taught as coming from God; we receive his commands, and rely on his promises, as the commands and promises of God. In his miracles we see the power of God; in his doctrines and precepts we behold the wisdom of God; and in his life and character we see a bright display of every divine virtue. ...