Two major reasons to get this: 1. You always have your iphone with you, so it eliminates the need to carry an additional pocket-sized dictionary around with you; 2. If you enter some conjugated verb, it will tell you what the verb is -- for example, type in 'fu' it it tells you that it is a form of 'to be' (it is the 3rd singular remote past). No small print dictionary does this -- try to look up 'fu' in a pocket dictionary and you don't get anything (though some of the bigger and better print dictionaries have SOME odd verb conjugations listed, but this has all of them, as far as I can tell). This is very helpful if, like me, you don't have all the many tenses and conjugations memorized.
However, there are 2 things that keep me from giving this a 5/5. First, relative to the last point, while it will tell you that, for instance, 'fu' is a form of 'to be', it doesn't tell you what form. You need to click on the conjugations tab, and then go through the different conjugations until you see where it is. This only takes 30 seconds or so, but it could be much easier. Still, a print dictionary won't even tell you what verb it is. But even so, it seems that instead of just telling you that it is a form of 'to be', it could also just tell you the conjugation. Presumably it knows this information in order to tell you it is a form of 'to be' to begin with. Second, it is not a replacement for a BIG, GOOD print dictionary, since the entries it has don't go into the kind of detail and examples that a good large dictionary will. Again, this seems correctable. Just adding a few megabits to the file size.
If they were to make these two very makable adjustments, this application would be an amazing product that could replace even large good print dictionaries. Hopefully they will. Then I'll change my score to 5/5. But until then, it still is extremely useful, easily merits a 4/5, and is well worth getting.