Compatible/incompatible, reliable/unreliable

The plug fits the socket.
The plug is compatible with the socket.
The plug does not fit the socket.
It is incompatible with the socket.
This printer has never broken down.
It is reliable.
This printer often breaks down.
It is unreliable.

Which word best describes the following situations:

1) This program sometimes crashes.
It is

2) The data output from this application is always accurate.
It is

3) This app will run on an android or an iOS device.
It is

4) This e-reader sometimes loses my place in the story.
It is

5) This app does not work with older systems.
It is .

6) You can have confidence in this system.
It is