Scratchy? Stoneware for the privy
Why I don't believe it's use...There would be thousands if not more of these things found if they were used for what they are saying.
Depending on the shape (I can't tell by these horrible photos) I could see a skin scraper (exfoliation). Those were used in bath houses in the middle east and could see the Romans stealing that idea to make their own of sorts.
This is always the challenge for a historical potter just figuring out what to trust. I have numerous books printed many years ago that have wrong information (newer books have proven opposite info) and vice-versa. Over the years you just have to go with those ideas that make the most amount of sense to you and hope for the best.