Could you be more specific about what it is that you'd like to know?
Is it, how the crystals are formed? Their purity (mineral salts could co-crystallise)?
Or experiences of their effects?
More generally, growing crystals by evaporation is something of a standard procedure, but it's still good that you ask about this simple, solvent-free (besides water), base-free method. Perhaps it seems almost too good to be true?
Short boils on fresh cactus material yield a purer product. To keep the length of the simmering time an absolute minimum, cut the cactus into paper-thin stars after removing the waxy cuticle. (This is different from step 1 of House's.) Time invested in cutting is paid back in shorter simmering times and a correspondingly lower energy usage.
Burning the spines off with a blowtorch also causes the skin to blister up slightly, which may ease its subsequent removal.
I think crystals are more likely to form if you happen to chance upon a cactus with low mucilage content. I've never produced crystals like this, but then again that was never my goal. Different species and varieties of cactus can yield different qualitative effects as well.
It would be interesting to compare the effects of the crystals with those of the unevaporated brew.
The instructions seem pretty clear to me, just follow them and be sure to report back.
You've piqued my interest
“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli