They would like to invite customer to factory tour, so unit appearance is one of the factor for decision. 聼起來自然嗎?

They would like to invite the/a customer on a factory tour, and so the appearance of the machines has become one of the deciding factors for giving the tour.

I added the/a because it's a "count" noun
I used machines because unit could also refer to staff. Machines sounds less ambiguous. Also based on you sentence in Japanese, I think this word fits better.
'Deciding factor' is a simpler way of saying factor for decision
I added "for giving the tour" to provide clarification on what decision is being made based on the appearance of the machines.