I don't understand why you need options at all... If you point it at a file/directory it should automatically compress and if you point it at an archive it should automatically decompress. The options should be there for advanced tasks not 90% of the tasks you need the app for. It's really poor ui design.

After googling this three separate times I finally just aliased it to an 'untar' command. I'll remember this for when I'm ssh'ed somewhere!