These look very strong and are good and adjustable, there's a locking screw to stop any unwanted horizontal movement.
A locking screw for up and down tilt too. These are good for any smaller venues to save stage floor space of speaker stands.
Unfortunately one of mine arrived with broken bushing, will have to return it for repairs, but I know this will not be a problem with these guys & will receive a replacement before week end.
Apart from this problem, these look great & when attached to the walls in a secure manner will be up there for a long time for many bands to drop their PA speakers on.