With romanian you bend your knees a bit. This reduces pressure on the lower back greatly while still slamming your hams.
Not nearly as much as for a romanian deadlift.
Romanians you bend you knees enough to go close or all the way to the floor with SLDL you just go as far as your flexability allows.
True Romanians you don't go to the floor either.
Romanians there is more of a bend and you really push your hips back at the bottom while arching the back hard.