I'm not a Unitarian, but when one claims that there is only one God, and then starts talking as if there are more than one, it becomes confusing to some. So I don't blame them for taking their position.
Your point with regards to contrasting God with idols is interesting in that idols are worshipped as gods, yet when Paul says that Christ is the image of the invisible god, he doesn't use the word "Idol" therefore Christ cannot be worshipped as a god. Instead, he uses the Greek word "eikon" (i.e. "Icon") which means that Christ represents God because that's what icons are. They are representations or representatives. They are like dignitaries or ambassadors from another country and are equivalent to the king, President, etc. in their authority abroad. Their words are the words of the king, President etc. They represent the person.
Jesus Christ represents the person, but God cannot be distilled down to a person. This isn't to say that God cannot be immanently present in a person, or even within all of humanity and this is precisely what happens after Christ returns and along with the elect, returns to the father when all are one.
Paul's insight in 1 Cor.8:6 is the most enlightening to me in that he distinguishes between God, the father who is the origin of all creation, and Christ the son who proceeds from the father and is the means of everything created.
He clearly distinguishes God from Christ, so if we're going to conflate the two, we can conflate all aspects of God as well. We don't do that which spotlights that we're still not being honest with ourselves. We're not any closer to understanding who Christ is than anyone else.
When we look at an image whether it be a painting or our reflection in a mirror, neither the image nor the mirror are who we are. Likewise, the persona that we construct and is identified with a physical body is no more who we are than any of the numerous component parts. Add them all together and we still don't have a complete picture.
When a person dies, we say that they have passed on, yet their body remains, and to a certain extent all of those ideas we associated with them still remain to some degree in our own minds. They are nothing more than ideas, and that is all they ever were.
In the same way, whatever ideas we may come up with for God, Christ, etc. are always going to be just ideas, hence the biblical prohibition against idolatry, or image-making. Our imaginations will never come close to knowing who God is.
The biblical authors simply point out that if you want to see the face of God, you need to look at his image, and that can never be seen unless or until one receives God's spirit.
At that point, it's difficult not to see God everywhere in everyone one comes in contact with, and this is exactly what Jesus taught, e.g. "whatever you do to others, you do to me", and "apart from me, you can do nothing".
So when we deny our persona, or ourself, Christ is revealed, and we begin to see others as God sees them through Christ.
Christ is the Symbol, Metaphor, Icon, mediator, medium, copula, image, means, representative of the transcendent God, but by definition, none of these things are God.
In a nutshell, even though Christ isn't God, for all practical intents and purposes, he might as well be. You can't look at God without looking at his image. There is nowhere else to look. Moreover, one cannot see God unless it is by the power of his spirit dwelling within.
This reveals a trinitarian reality which should never be conflated or confused with a trinitarian god.