So, we investigated in chat for a bit.
Right now, it downloads the maps to Steam\SteamApps\workshop\content\440\<MAP WORKSHOP ID>. That map is already playable if you copy it over to the maps folder.
There currently seems to be no automatic sync with TF2, so you have to manually do that by typing tf_workshop_map_sync <MAP WORKSHOP ID>.
It will then be startable by typing map workshop/<ORIGINAL FILENAME>.ugc<MAP WORKSHOP ID> . There is currently no option to create a local game with that map without using the console, and autocomplete won't work (because of the subfolder, i guess.) So basically, it's working, but there are a few steps in between missing.