From what I've read, g-tummo is very likely not the Wim Hof Method. I've never trained with a monk claiming to know g-tummo. The son of Wim Hof loudly told me "The Wim Hof Method is not Tummo!" (almost a direct quote from memory, probably paraphrased). So I'd argue that back in 2014 or whenever it was, they were of the opinion it was something else. I'd be willing to bet they've never met a g-tummo monk either :)
A good medical YT vid on the WHM [1].
From my experiential point of view: the WHM doesn't warm your body, you simply don't get cold, nor do you feel cold (you're too high on adrenaline to have any normal sense of temperature). Sometimes I did feel a warmth boost, but that's not the main "working thing" behind his method. I use it whenever I need an adrenaline boost, or don't want to feel cold.
When is it handy or fun to get an adrenaline boost on purpose (my experience)?
1. When you have a headache (free painkiller when nothing is lying around)
2. When you're at a party (no drugs needed, the WHM is a drug in its own right)
3. When you're having sex (a lot of adrenaline kinda changes your personality a bit :) )
4. When you're cold