Those ‘U’ hangers are very good, there are lots of different types, i use the ones that have a locking bar that snaps over the front to stop the guitar falling off.
The parts that touch the guitar are covered with a spongy material so it wont mark the neck.
Hanging a guitar by the neck will not harm it in any way, make sure you don’t hang it near a radiator or fire or in direct sunlight, just use a bit of common sense.
What kind of guitar is it? tell us a bit about it.

Lee.