They are a good exercise, I wouldn't say "as good" as squats, but it'd be a good addition to your routine. Barbell hack squats of course, not the machine. However it's pretty tough to get your form down, it takes quite a bit of practice and work on your form
I have also heard of a lot of guys tearing their ACL trying to use a lot of weight on a hack squat machine. Be careful with the form and keep to higher rep ranges if you use a machine.
