I don't remember what all of them are (used to program quite a bit in AppleScript, but have forgotten a lot since starting law school), but Script Editor introduces a few bugs when it creates bundles. One big annoying problem is that when you have a "bundle" applet and ask System Events for the currently running processes, the bundle is named "applet" - NOT the name you gave it. Non-bundled applets properly are referenced by the applet's name.

There are also issues dealing with this buggy behavior when you're trying to handle both Panther and Tiger, since System Events in Tiger has a new property for processes that you can use to work around the previously-mentioned bug.

Anyway, I'm assuming that's what the developer means, but don't have time to test it out. If you haven't come across the bugs, perhaps you don't need this.

Then again, Script Editor does not let you specify the short version, etc. of your applet bundle and this does. If you take a Script Editor-created bundle and modify the Info.plist by hand, then save again from Script Editor, I believe it wipes out those manual customizations.

Basically, it sounds like this Script Bundle Tool is very useful if its description is accurate. Too bad it didn't exist back when I was actually writing AppleScript programs often.