I'm curious about how safe these metal toys are to use

Stainless steel will always be the safest toys to use but unless you have a metal allergy, aluminum shouldn't bother you. The metal itself shouldn't harm you in any way. It rates an 8 on EF's safety scale. Personally, I'll stick with stainless steel for metal, but aluminum is safe to use unless you're allergic to it. Allergies to almost any substance are nearly always possible but aluminum is such a common metal (used in a lot of drink cans and other food containers) you've probably been in contact with it at some point. It's also worth mentioning that aluminum is found in most antiperspirant deodorants. Now, there's some concern these days that mainstream antiperspirant/deodora nts aren't totally safe, but that's a topic for a different discussion.

The Tantus Alumina dildos are made with "Anodized" Aluminum, as long as you clean them with soap and hot water, and not some hardcore sterilization methods that might damage the coating, you shouldn't be worried about any allergic reactions to the material.

We have the Alumina Flow and have used it frequently for several years with no issues. As indicated above the anodized finish makes it nearly inert - and we always use it with lube - so there is little metal to skin contact.

Stainless is great - but the Alumina line is safe as well.