I’ve never tried Wim Hof’s techniques — I’d like to — but I have practiced bhastrika a good amount and do nadi shodhana every morning before meditation. Does his technique really resemble tummo? I’ve tried to find a tummo teacher (haven’t found one), but I’ve read “The Bliss of Inner Fire” and from what I understand a fundamental part of it involves mula and uddiyana bandhas being engaged in conjunction with the “vase” breath. Does Wim teach these things? I’ve seen photos of him practicing and he’s definitely doing uddiyana bandha, but I’d be surprised if he teaches that, it requires deep transverse abdominis activation to do. I only started getting that awareness in that layer of muscle after a couple years of yoga practice.

If he’s not teaching the bandhas then the technique really is just bhastrika with retentions. It’s a totally great practice, but I’d say it’s just the beginning step in the path of pranayama practice.

You make a great point. I think you are right in your classification. But the basic point in my comment was that the Wim Hof technique is simpler than Pranayama, and is highly beneficial in itself. Pranayama is very technical, and I am always worried that I am "doing it wrong".