The trouble with ? dictionaries is the fact that you can't use it if you don't know much of the language as you won't understand the ?. A low level learners' dictionary on the other hand will help with easy words, words that have ? like table or chair or apple.

The other nice thing from a learner's point of view is that even using one at a low level gets you into the habit of using a monolingual dictionary and more ? students should be using them as much as possible. They give a lot of information about the word; how it's ?, grammar points, if it's ? or ? and so on.

You get plenty of ? in a monolingual learner's dictionary as well, how it is used ? and what other words are used with it.

You have to be careful about ? dictionaries because the definitions are less clear and the other information that you'll find in a ? isn't always there.