No, but they are a great add in after squats. Nothing works like heavy squats for leg power. You can actually tailor your hack squats to hit different areas, where squats are a basic compound movement for overall leg power and strength. You can vary your footing slightly on squats, but you have much more control in isolating areas with hack squats, plus no fear of adding weights or having a spot.
-------------- Failing to plan is like planning to fail!