I've used this method for workout and it's quite good. I've also followed others of Wim Hof's routines for meditation and relaxation, which are awesome. It's important to note, however, that although he has popularized these exercises and his approach in certain instances is indeed unique, he didn't develop them but merely adapted them from powerful breathing techniques used in Yoga for thousands of years.
Estupendo post, muchas gracias por compartir tu experiencia, José!