I read about these on another site and i think they make an interesting change from regular calf raises.
For these instead of standing directly under the pads, place your feet about two feet behind the pad so you are leaning forward. You will have to adjust the pads so that they are lower and the weight stack so its a bit lighter. You will now find that your starting position has you already in the deep starting position you try and reach with regular calf raises. You should find these give you a slightly harder job getting the weight up due to the fact that you are pushing forward as well as up. Dont use the block as it could be unstable at such an angle, and it isnt needed anyway.