How does the Mizzium Apparatus's ability to serve as an arcane focus interact with its ability to let you cast a spell you don't know/have prepared?

Question

I recently got to DM my first campaign, and I was planning on letting my players get their hands on a Mizzium Apparatus. However, reading what the Guildmaster's Guide to Ravnica says about the item, there is one main point I am confused about.

For those that don't know, it states that the Mizzium Apparatus can be used as an arcane focus while being worn, but it also has the ability to let the wielder cast any spell without knowing or preparing it, as long as the spell is from their class's spell list, they have the appropriate level spell slot, and they provide the required components.

I know that this means that they still can't cast spells with verbal or somatic components if silenced or bound, but how does this work for material components? An arcane focus is used to replace the material components of a spell, assuming it doesn't have a listed cost and isn't consumed.

Would the Mizzium Apparatus still work as an arcane focus for these unprepared spells, meaning they don't need to pull out an arcane focus since it's equipped? Or would it only act as an arcane focus for their prepared spells? Or is it up to DM's discretion with no set rules?

Answer 1

The arcane focus is a required component for spells that have a M component with no listed cost - there’s no reason they shouldn’t be able to use the apparatus as a focus for itself.

Answer 2

From my understanding, the line: "and they provide the required components." would just be referring to components that a focus can't replace, like ones with a cost or that are consumed.

As you stated the Mizzium Apparatus is an arcane focus so it automatically accounts for normal (no cost or consumption) materials, and that line in it's rules would just be to remind people to provide non-foci materials.