This app is used for two purposes:
1. You open a file and when you select an app it is automatically selected as the default app. You want that you must be presented with an app chooser every time you open that file.
2. You want the app chooser to pop up but you don't want to press the JUST ONCE button every time.
The solution to this is that you need to go and open the file as before, but instead of selecting the desired app you should select APP PICKER.
Then you will again be presented with a list of apps which can open that file. Now you can open that file with your desired app.
Next time you open the file, you will be presented with a list of apps which will also include the App Picker. Now you would not need to select app picker again.
Your problem should now be resolved, that (1) you will always be shown an app picker, and (2) you will not need to press JUST ONCE button.