I understand the temptation to go Hardman, with Hill out, and a good matchup. Anderson missing Darnold makes this seem like two players going in different directions. That said, I'd still go Anderson. i don't view the Browns as a bad matchup, and Trevor Siemian has plenty of starting experience, and at least initially might not be a downgrade from Darnold.
I really just want to see Hardman do something before I trust starting him. He could play every snap, and do almost nothing and it wouldn't surprise me, with Kelce, Watkins, and the RBBC there.