I have a commercial sized metal roof that needs repair. I'm thinking about an overlay. Does anyone have experience or opinions on these.

Let's get some more detail. What kind of commercial metal roof do you have ? U panel, R Panel, 2" structural standing seam?

We've done them and there are options. For example, a dilapidated exposed fastener R panel can be overlaid with standing seam but filling the original panel gaps with structural and insulating products to creat a flat surface to attach the metal to. It prevents having to demo and tear off and provides additional insulating properties to the roof and you end up with a new metal on top. It's done frequently. It's a thing.