The dartlang plugin (the plugin needed to have Dart integration in Atom) is very buggy, even for a new software. One of the most annoying things is that the analysis server does not work correctly.
Issues · dart-atom/dartlang
You can try to use it for the productive work (for several weeks) and you will understand that this plugin works very buggy and it are very limited in features (practically nothing interesting and with bugs).
Main feature is in that the it uses analysis server and even it works very badly (see all issues on bug tracker).
I use it and I am not happy with only because it very buggy and very limited as source code editor.
Eg. I am even does not know (using dart plugin) how to implement unimplemented members in a class which extends (or implmements) abstract class (and many other missing similar features).
I answered you to your question, and let me ask you: "What is the purpose of you asked me about it?".
To see if these bugs you experienced are reported as issues in the project Github
What kind of bugs did you experience that were a deal breaker?