BlueJ is very easy for Java beginners who want to start programming without learning how to use a more complex IDE. Besides, BlueJ allows seeing how objects are created. I find useful this tool for new students. New users only have to create a project and then they can begin to create new classes and write code.
It does not autocomplete code, which is essential if you want to use an IDE for complex programs. Moreover, it does not provide any debugging option, which is essential when you are writing more complex programs. On the other hand, it does not provide an interface for building Graphical User Interfaces (GUI). Instead, you have to write your own code, execute it and then test different parameters as for example size, captions, types of buttons, etc.
I recommend BlueJ only if you want to start programming without learning how to setup an IDE. With BlueJ, you just have to write code and execute it, without problems about classpath, projects, etc.
If you have already used other Java IDEs, then you have to adapt to BlueJ in the way that BlueJ does not offer autocompletion of code. So, you have to be very careful when closing code blocks, parenthesis, etc.
It is also important to remark that the fact of creating objects just in BlueJ, does not mean that your code is creating those objects.
Education. It allows showing how objects are produced as well as methods and attributes of objects. It is useful for introducing Java programming