That's good advise, I don't think an electronic E6-B is ever good in flight, they are too difficult to be used one handed. However, for preflight planning, they are very useful. Most can do functions that a manual E6-B cannot do.
However, this is not an excuse for not learning how to use a manual E6-B. On the contrary, an electronic E6-B is something you move on to (in my opinion) when you have mastered a manual E6-B.
I whole heartedly agree with your chief flight instructor, digital is not good for inflight use, but on the ground, its a whole different story.
"A pilot's plane she is. She will love you if you deserve it, and try to kill you if you don't...She is the Mighty Q400"