It could clip on the bottom of the mac as the rubber grip pads are replaceable on both sides. Trouble is the device leverage is gone as normally it would swing to the side where the display is. On the bottom it would want to swing out. If the phone is light enough the grip might hold it, but if you're interacting with it without gripping the device you could have problems. Doubt a tablet would have any chance.

I've used one in the past prior to purchasing it and can't wait to get my own (should be sitting on my doorstep as we speak). It holds a fair amount of weight with a tight grip. You would have no problem hanging an iPad mini on the side of your display. Anything bigger will be unwieldy. The real issue is how much weight can the hinge of your laptop display hold with the device hanging off the side, while tapping the device. My macbook holds up just fine.