Vai uses the back stop more for stability with double stop bends. Joe satriani doesn't use it at all. When you bend any string the others will go slightly out of tune, a back stop greatly improves this issue.
I never understood the logic behind this when it came to the Backstop. When you bend strings, it pulls the trem block away from the Backstop, which still allows detune to occur.
The only exception is the Hipshot Tremsetter, which actually attaches to the trem via one of the spring holes in the trem block to hold it still until you overcome spring tension.
I have tried several different styles; Hipshot, Backstop, Arming Adjuster, they always came back off and sold. I guess they just aren't my thing.