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Mounted to your goodman light handle, there are no bubbles, its allways aimed at the light source, image is always stable (if you are), and won't be flopping aroung or dragging on the bottom.......Your scheme is creative, ingenious, and novel, but probably terrible. Good luck.
There is just something about attaching a non-essential accessory to a second stage that doesn't feel right. I could say it might get in the way if you must donate primary or need to recover reg from behind you but that's reaching. I can't put my finger on it.