Overall:

I have raised a few minor comments but otherwise this is ready to merge, with +1 for a clear and detailed deprecation message.

Notes:

flake8 uncovers that that there is still a reference to _mask_fpe, but as you have implied it is in _binary_operation which I am covering (PR to go up today or tomorrow) so not touching it here to avoid the merge conflict is wise. I've already removed the reference to it in my branch for the PR.

There is one other undefined name though, maybe we can deal with it here whilst we are here? It's in get_filenames which is marked as migrated in the big table:

flake8...................................................................Failed
- hook id: flake8
- exit code: 1

cf/data/data.py:4181:20: F821 undefined name '_mask_fpe'
cf/data/data.py:9406:30: F821 undefined name 'FileArray'