No safety net: mistakes are not highlighted while you type. Fill in the grid, press Check, and find out how you did.
The puzzle rules are the classic ones: every row must be a real word that gives exactly the colors shown, and found letters must be reused in the rows below.
The difference is the feedback. Red corners appear only after you press Check, and they disappear again as soon as you change a letter. Hard mode rules can't be switched off here.