I have the humbler with the ankle cuffs myself. As you say, you definitely feel is presence when you’re in it!
That being said, we don’t use it all that often, only on the special occasion when it takes her fancy to have me more … obviously compliant. 
Already got into light stuff etc and brings us both immense pleasure during and for the end result,doubt we’ll go any rougher the heels thing is a big turn on for both of us but doubt we’ll really implicate it much further than her wearing them and some light taps whilst wearing them the stilletto to the sack is nice idea and a turn on for both in reality is to far and a risk,knee has already been tried and also worked and caused no issue but she doesn’t go full force crazy but gave enough for us both to be happy and carry on
One of most intense orgasms for me recent was my balls in a cock ring making love doggy style and she squeezed when I was nearing the end and just wow that was intense like she squeezed out every drop from me and massaged them after which brought on alot more leakage I suppose would be the wording
That’s abit to far for us that’s quite brutal I think but each to their own I guess
There’s a lady on this forum who likes having her nipple pierced by needles.
Not far off from a small nail through skin.
Neither would be my thing, just saying there’s variety all round.
I have my own vice (rough nipple “play”) thats not gonna please everyone. No skin piercing for me though.