Outside of the classroom, I don't see the point of this dictionary (we have the 2009 version). It's missing a lot of words, in fact the few times we used it, the word we wanted was missing. Instead of teaching my kids to use a dictionary, it annoyed them that the effort to find the word was in vain.
I would go with a children's dictionary aimed at a slightly older audience, which is a good sacrifice even if you have to help a five year old with reading it, because it will last you much longer and contains a more complete set of words. I don't have the money, time, and shelf space to buy something that has such limited use. We got the Thorndike Children's dictionary and it has worked well.
I can see where some kids may pick it up and read for fun, but honestly even there you're better off with a Children's Illustrated Encyclopedia because this has limited information per entry (as expected from a dictionary). Early readers may get some use out of this, but by the time a child is 6 or 7 they likely have a vocabulary that exceeds this dictionary.
On the flip side, the definitions aren't simplistic enough for five to seven year olds. I don't like dumbing things down, but to define a "loudspeaker" for example as a "device that turns electrical signals into sound" just adds a whole new set of questions to a 5-7 year old's mind instead of telling them what it is. You could use this as a launching point for discussion, but I use it to help my children figure out how to look up words for themselves, not something that confuses them further.