Just so there is no confusion, I am only answering this question.
Is it safe to connect multiple duplex receptacles 120 volts and 240
volts on the same circuit?
When you say safe do you mean will it cause a burn or shock hazard causing an injury or death? Probably not.
But if you are asking is it safe use this circuit and not cause any damage or failure to the circuit or the equipment used on it? It is not safe.
In simple terms. Using two different pieces of equipment one a 240V and one a 120V on the same circuit will cause an imbalance in the circuit.
Example: One piece of equipment is a 240V motor pulling 4.7A and one the other is a flood light pulling 3.3A. One leg of the 240V circuit is pulling 4.7A and the other leg is pulling 11A. This creates and impedance in the circuit which the causing overheating and an imbalance in the 240V motor reducing its life and over heating in the conductors reducing their life. I know there is more than that, but as I said I want to keep it simple and short.
So, from a design standpoint, it is never a good idea to have multiple voltage device circuits unless all equipment is designed to work in tandem.
Hope this helps.