What do you think?

It shouldn't damage it, but I don't like the idea of attaching anything to the shroud or air cylinder. When I had a Regal I used a Harris bipod attached with a simple stud in the forend. 

I'd be concerned about POI shifts-you could torque the airtube and barrel.

I think they ought to clean up their back yard a bit.

As for the item at hand, I don't think putting it around the Air Tube would bother me, but probably not around both Air Tube and Barrel/Shroud.