One of the most useful accessories I have in my darkroom are two "Softener" (that's all labeling they have) filters. I bought them on a whim from a "miscellaneous" used filter box for very little money - mainly because they were 40.5mm filters - just the right size to fit my Rodenstock enlarging lenses. They work *beautifully* in printing portraits.
I now rarely use the Hasselbad "Softars". There is more flexibility in keeping the sharpness in the negative and softening the enlarging image as needed.