This bracket is pretty flush to the wall. 4-5 inches at best. I have it on metal posts and has not failed yet. As long as you follow the weight bearing limits, you should be good. If you are going to metal (depending on the thickness, you want to go with a butterfly type bolt system.
I needed something very narrow, and very flat - I was hanging a 48" TV on its side. This device let me do just that. Very thin, so it hangs close to the wall. No frills, but I absolutely was not looking for any! I don't have a photo of it complete yet (must finish in-wall clockbox) but would unconditionally recommend for anyone looking for an LED/LCD photoframe mount.