I'm using ToodleDo Sync which works fine in most respects.
I've set up an extended Outlook field called 'tdfolder' which is set in the sync program to be used as the ToodleDo folder.
If I create an item in ToodleDo and give it a folder, the item is created in Outlook and the 'tdfolder' field has the right value when I synchronise them.
Going the other way, it works if I create an Outlook item and type an existing folder from ToodleDo into the 'tdfolder' field. But if I put in a new folder name, which doesn't exist on ToodleDo, the Outlook item is created with no folder when I synchronise them.