This is the best 6 pages of "how to understand using stuff to control humidity" on the intrawebs.
The RH over distilled water is 100%, for what that's worth.
The guys have told you about other things, many that use compounds and or chemicals to lower that 100%.
All kinds of salts can be used to lower that 100%.
HCM beads work completely differently. They work via a lot of math, covalency, and equilibrium.
Everyone likes what they like, as long as it gets the job done.
If HCM beads didn't exist, I'd use Heartfelt beads. I also use Boveda packs.