Electronic dictionaries are generally bad for the classroom. Students just can't resist using them when they get new words. They could be used, provided there is some strict guidance at the start of the course as how and why we use dictionaries.Most often, without proper guidance it becomes frustrating when my students (who are quite keen to learn) head for their e-dictionaries when I have just only mentioned a new word. Sometimes it takes away focus from the subject as some new words are just introduced but not as part of that lesson ( I call them throw away words).This is when I get to ban them. Also, often using these dictionaries could mean that the students need some non-dictionary vocab learning skills. Read
my article on this topic.