They are similar, but they are not the same exercise. First, the Hack Squat engages more muscle groups than the Leg Press. As the weight is supported by your shoulders, you will be activating your core more than when you are doing a leg press.  The range of motion is much better on the Hack Squat. On a Leg Press you can only go as deep as the part where your thighs meet your gut. If your Hack Squat Machine has the necessary range of motion, you can go “Ass to Grass” if you have the flexibility and strength.   You can lift more on the. the Leg Press up. The weight on a leg press traditionally moves on a 45-degree angle.  Most hack squat machines have a steeper incline which will make the load heavier. Also remember that you have move your own bodyweight on the hack squat too.  The leg press is a great leg exercise for beginners. Some would say a safer alternative to the traditional barbell squat. The Hack Squat is generally used by more experienced lifters. The best choice will just come down to your training goals.