Upload & Sell: On
I have the Magic Arm, and like it, but never use it with large loads. A lot of monolights will exceed the rated capacity of either of these, so as stated above, it all depends on the monolight and modifier.
Having a grip head on a super clamp may be a better way to go for larger loads. You do not want to get a load out too far away from an autopole anyway, because it has the potential to lose its grip and slip. Here is a link to one:
You can use a short pin in a grip head, or consider a longer rod, or even a rod with another grip head on the end. If you use a rod, you could even add a counterweight to the other end to keep the load close to balanced at the autopole location.
C stands are really what would normally be used for monolights with modifiers. They are usually pretty heavy to start with, and have legs that are very easy to put sand bags on. And the legs adjust in ways that allow two stands to be placed close to each other, or adjust the leg postiions to move them partly out of the way. And when you are all set up, and ready to shoot, a C stand can be relocated for different lighting fairly easily, but an autopole is a royal pain to move. Safety is another big issue. It is easy to check a C stand to see if it could tip over, but a monopole can not be checked, and could just come loose at any time. If you are putting big gear near or over models or customers, it is part of your job to keep them safe.