I suspect the product only causes immobilization, ie paralysis. "When used properly, it induces a temporary state of immobilization"
I doubt you would want to be just immobilized during the process. In medicine we give a sedative and paralytic so the patient is not aware while in a state of paralysis.
Besides PETA, who says fish feel pain anyway. I don't believe there is any solid evidence on this. It is more a human response to percieved suffering. Would any method be more or less painful than being eaten in the wild by say a barracuda?