feralcomprehension
Qualified Observer
Respectfully disagree; stainless steel is significantly harder than (typical) anodized aluminum and is far less likely to lose material off the teeth.The only way to guarantee there is nothing "extra" in your herb is to shred it with your fingers.
Haven't seen a hard-anodized grinder; that would be a horse of a different color.
You can use aluminum if you want, but stainless steel is superior in this application given equivalent design.