I found web sites belonging to an interesting denomination, the Brotherhood of the Cross and Star. This shows what extremes can result when believing in the Trinity.

They believe the 3 persons of the Trinity are reincarnated in a family in southern Nigeria. They believe you have to wear white robes all the time. Wearing wristwatches is a sin (because it's jewelry), weeping is a sin (they have an article on why Jesus wept, because it was allowed before he was crucified!), going to doctors is a sin, eating meat, fish, eggs and dairy is a sin. Three times a year you have to fast totally for 72 hours, not even water is allowed.

Test every spirit...

Would they like the Brotherhood of the Cross and Star, just because it is Trinitarian, or would they agree with me that it is a false gospel? It seems to me like Trinitarianism can lead to greater extremes than Unitarianism (Arianism or Monarchianism).

even before the "Christian Trinitarianism", Trinity in various forms had been worshipped by Pagans...

Trinity is a product of Christianism marrying Paganism. The principle of God becoming man and dwelling among us was Pagan from the very beginning. Romans, being Pagans in the past and believing in Zeus, Hera and his sons, had great influence in developing the Christian counterpart - the Trinity.

The devil simply made Jesus Christ a god in eyes of most people and then, let people worship a different Jesus Christ.

still, that does not prove that God is not a trinity. He might be a trinity regardless of pagans think.

I am not defending the Brotherhood of the Cross and Star here. That is clearly a false gospel, believing in another Jesus. And it is just as guilty as other trinitarians of being dogmatic about Trinity. We should not be dogmatic about God being one or two or three or more than three. We should realize we don't know enough about God.