I gave this feature another try with a new set of external tools. It doesn't work with MP3Trinity and Free MP3 Cutter and Editor. When a few files are selected from the Main Panel or the Now Playing and sent to these tools no file is sent to a tool. The only result is that a few MP3 Trinity or MP3 Cutter windows are opened, but all the windows are empty.
Maybe these tools should be used with a parameter
Fortunately, Power Sound Editor Free seems to work fine with MB. In fact, when a few files are selected from the Main Panel or the Now Playing and sent to the tool every file is opened in a new window, which is expected behaviour for an external editor.Possible bugs:
1. When one external tool is replaced with another in the Edit/Preferences/Tools window the old tool name remains by default.
2. It's impossible to send whole Albums to an external tool (including MP3Tag) form the Main Panel when 'Artwork' View is used.