Doesn't Vibram pierce easily?
I have not had any issues with piercing with anything like glass, nail will probably pierce it but that will go through normal running shoe as well.
My suggestion is to take it slowly when you start, shoes that we wear make some of the muscles/tendons in our foot almost atrophied. With these shoes you gona use them and it takes time to build them back up. Another thing is bone density in the foot bones, you need to build it up so some of the smaller bones dont just snap