I was curious so I decided to give this nifty door lifter a try. It's helpful for lifting heavy doors just enough to screw the top hinge to the door. Of course it's only an extra hand, so you still have to lift the other side. It will Not balance the door for you. It has fairly good clamping power and ease of use with a few drawbacks.
Twist the metal rod toward the door and squeeze to lift.
Twist the metal rod away and the clamp releases. pretty simple.
Its fairly wide so for standard interior doors theres an inch of play that causes slop if the door is moved back and forth (while installing a lock set on a installed door) Also it does not hold very solidly on slippery surfaces well.
The unfinished metal rod hook end faces the door edge when lifted and has hit the edge of doors on a couple occasions. be careful, maybe a rubber tip should be installed on the end.
I wish the bottom pad was more of a softer rubber. It's made out of plastic. also the bottom of the metal tray is rubber door side and floor side. The sides are not padded.
I'm glad I made the purchase, but could see room for improvements. Hope this helps!