With all fixed supply models (bitcoin et al) the price is the variable.
With Radix the supply is the variable. Granted, the attempt isn't to "fix" the price, but to substantially smooth out the high volatility through autonomously generated supply based on the demand.
The real question is, why would anyone use such a thing over gold and silver? It's blatantly obvious no cryptocurrency is an actual store of value. How could such a thing be that doesn't even exist in the first place? That's why it has the word "currency" in the name cryptocurrency and not "money". All currencies are inherently worthless and go to zero on a long enough timeline, while only gold and silver remains. Since money is a zero sum game, allowing anyone to pretend to be god and act as a central banker issuing currency for profit is a master and slave dynamic. Hence anyone not using gold and silver is a slave.
Bitcoin kind of tricked people into thinking it replicated those dynamics of gold and silver, but in reality it's designed to centralize into a rent seeking usury system controlled by mining cartels, and those are the new central bankers. So the fact still remains, anyone not using gold and silver is a slave.