I constantly tell my students they should use their dictionaries as little as possible. They are ultimately frustrating. Far better to find material that students feel is comfortable, where they know about 95% of the words, so they don’t have to use the dictionary, and can still guess the meanings of the other 5% of the words.
But when one is surfing the web, at times, you need quick access to a dictionary because the web is not like a graded reader. The best I’ve found is Rikai translator.