This Hangman product is an excellent system for hanging anything on a wall, from paintings to mirrors. Once mounted, the object is not going to fall off the wall.
The Hangman system is two aluminum pieces, an angled bar that is attached to the object and a receiving bar that is attached to the wall. The two angles interlock and prevent the object from falling off the wall.
The 18 inch system will hold up to 200 pounds - not sure I would want to test that limit unless at least two of the mounting screws were in studs. The kit includes some small plastic anchors and self tapping screws. The object to be hung requires a fairly long flat wooden area. The top edge of a canvas stretcher or the flat edge of a rectangular mirror work perfectly. This cannot be used to mount a round mirror.
I love the security of this system and how easy it is to remove and replace the object (a mirror in my case). Mounting is not too difficult. It is absolutely critical to get the cleat on the mirror or picture absolutely square with the frame. Probably a good idea to drill pilot holes, the screws are short and fat and will probably split the wood otherwise. Unlike other systems, there is no way to adjust plumb once that cleat is attached.
Place the mirror on the wall, and mark the edge of the frame and the height where the cleat meets the wall. This is much easier than wire hanging because there is no sag. Insert the bubble level into the slot on the bracket (the level is a really cheap one with fairly wide imprecise marking). Line up the wall markings, level the bracket, and mark the screw holes. My mirror happened to be exactly 18 inches wide, so it was easy to get the edges right. If the mirror is much larger, no worry, roughly measure the distance to the edge of the cleat. Once the mirror is in place, it can be slid left and right a lot for final adjustment. Not a bad idea to locate one of the screw holes on at least one stud. If the wall is a normal wall, with 16 inch center studs, a second hole will hit a stud.
I like to use a small drill bit as a pilot hole and to test for a stud. When I find a stud, there is no need to drill a bigger hole for the plastic anchor. The slightly tricky part is getting that wall bracket perfectly level. The bracket holes are a little bit bigger than the screws with a little bit of play. Once two screws are down tight, the rest goes easily.
The one part that I don't like about this system, the mirror or picture ends up about 1/2 inch away from the wall. The mirror either has to be shimmed out with felt pads or something else at the bottom, or attached to the wall with some kind of adhesive tape (like 3M command tape). If it isn't shimmed or attached, the mirror will tend to flop around.
That little tiny 1/2 inch problem is my only complaint with this system. Otherwise, it is the strongest, safest hanger I have every used.