Go built-in if you can and use location specific metadata folders (maybe just as easy and certainly cheaper!) posted from another one of my answers here:
You can create a folder or series of folders and use location specific
default values for your metadata column to assign the managed metadata
terms depending on which folder they are dropped in.
Once you drop the item in the folder and the metadata gets assigned,
you can then move the files out of the folders and the metadata terms
will remain. Alternatively, you could just view the library with no
folders, but the folder will still appear in the url path for the
document, so I recommend just moving them out of the folder.
You can set-up "Location-Based Metadata Defaults" by going (from the
ribbon) to Library -> Library Settings, then under General Settings
select 'Column default value settings.' On the left-hand side you'll
see a list of your folders under the heading 'Location to configure.'
I will typically create just one folder and change the default value
depending on what items I'm uploading, but you could create multiple
folders for whatever terms you want to assign.
Once you have this setup, you can bulk upload files into the specified
folders and they will automatically be given the corresponding
metadata values for that folder.
You can then easily move all of the items out of the folders you used
to give them default metadata values (so that you have a flat library
structure). Also worth noting, my other answer addresses text/choice
fields specifically, but this technique works for all kinds of fields,
including managed metadata.
Useful to note this works for all data types (including managed metadata)