Personally, I prefer triggers or dedicated buttons. I've never heard of the "using the firing trigger when in close range", but that seems like an interesting idea that I might like.
If you have a copy of mass effect 1, or gta 5 , you can experiment with this tactic. Just so you know i had a difficult time trying to gunbutt somebody in gta 4 because of the strange controls. Not sure if its better in gta 5.