I recently tried to squat using the squat calf machine and I found it very practical and efficient for when you are training alone without a spotter.
I have few questions:
On a side note, does the Inclination of the feet stand in the "squat calf machine" serve for sthg? or is it just a matter of shape/design?
There is a very low probability of knee injury while squatting if you keep your knees tracking parallel to your feet, and descend to a depth that places the top of your thighs slightly lower than parallel to the ground. The same is true for leg presses (and I will assume also for the machine you're asking about).
Two references that demonstrate the lack of ACL force during a squat or leg press are listed in this answer.
With a machine, the path of the weight is defined by the mechanics of the machine. You are not responsible for controlling the path the weight takes, only for pushing the weight along that path. This makes the machine exercise an easier exercise than the barbell lift. It is also less functional. You will need to use your back and abs more when you do the lift with a barbell.
The path that the machine defines may not be optimal for your particular limb dimensions. When you lift a barbell, you can move it in a way that is optimal for you. (For a squat, this means keeping the bar directly over your midfoot, you'll be sitting back, with your knees not extending too far past your toes.) When you let the machine define the path, that path may vary from the optimal path for your body.
