ok, my bad I think...? somehow I was getting an older version (I was wondering why the docs didn't match).
If I create a new project and do NOT import from the "create new project" dialog but do Assets->Import Package->Custom Package and choose 2dtoolkit2.3.3.unitypackage from my download folder, it seems to work.
I'm new to unity and I was under the impression that double clicking ".unitypackage"s will install them so they can be chosen from the import package dialogs... but doing this seems to get me an older version?