I have a Klann spring compressor aftermarket copy and I don't understand how it can "slip".
He either did it incorrectly, or that is a very, very poor compressor badly designed. The plates look different from my one.
Once the plates are in place, the compressor locks them in so they cannot rotate.
Vice Grips? Really? Come on...You are asking to lose a finger, or worse. Hope he has a medical power of attorney when he's in a coma at the hospital
Scary video...