The other reviewers appear to address the printed version rather than the Kindle-specific version. I am focusing on the Kindle Application.
Strengths -- easily used under Kindle platform, terse, usually is clear in distinguishing parts of speech, and it can be used as the default dictionary.
Weaknesses
1. Definitions are not necessarily any more complete than those from the New Oxford American Dictionary(already built-in on Kindle). Several that I used tonight were less so.
2. Definitions for one part of speech are often dependent on another definition listed for another part of speech (a weakness of many dictionaries that is annoying for more complex or unfamiliar words)
----Simple example: the word anger is both a noun and a verb, Thus they define the verb form as "to make angry".
3. Thesaurus component is okay and gives additional ideas for the verb "anger". However antonyms are very limited if the purpose is to use this as a writing resource. Very few choices.
----For example: antonyms for anger (verb) were delight, gratify and please. But other common options are missing such as calm, sooth, pacify. One would have to keep browsing and unless you set this as the default, you keep ending up in another dictionary when trying to do that.
4. Word Origins are sometimes given, mostly abbreviated and with less detail than in Kindle's Default Dictionary.
I have not compared word counts. Sheer mass of definitions is a misleading index of quality.