These are the best drywall caddy's I have used, and I have been doing this job for many years. They are simple, light weight and cheap.
All you have to do is cut your hole, just put the caddy up to the wall and outline where the hole should be.
Then cut the hole.
Next put the caddy up to the wall with the back side in the hole.
Now you have the two long tabs in the middle. All you do is bend one up and one down. As you bent the tab you are going to bend it again in the hole so that the tab is now tight against the drywall.