In the days when I had lessons, I was constantly getting bollocked for using the "finger wiggelling" vibrato on an electric. the party line was ... that is a nylon string trick not an electric trick. I have since learnt that that criticism was a bit harsh and that "finger wiggelling vibrato" does have a place in my playing. It is a subtle nuance not a smack in the face like the big old BB king style ! I find it adds sustain as well as adding a little vibrato flavor to a note.