So, I recently did my first campaign with DM and I intended to let my players get their hands on a Mizzium device. However, reading what the Ravnica Guild Master's Guide says about this object, there is one point that puzzles me. For those who do not know, it is indicated that the Mizzium device can be used as an arcane focus when worn, but it can also let the wearer use a spell without knowing it or prepare it, as long as the spell is from the spell list of their class, they have the appropriate level hex slot and provide the required components. I know this means that they still can not cast spells with verbal or somatic components if they are silenced or linked, but how does this work for hardware components? An arcane focus is used to replace the hardware components of a spell, assuming that it has no cost shown and that it is not consumed. So, does the Mizzium device still operate as a mysterious home for those unprepared spells, which means they do not need to shoot a dark hearth since it is equipped, or does it act only as a dark hearth for their prepared spells? Or is it at the discretion of DM without defined rules?
As a bonus, how would it work if they failed arcane verification and cast a spell on the list for which they could not provide components (for example, they were trying to launch Catapult, failed arcane verification and ended up throwing Chaos Bolt despite the silence)? If a warlock, wizard, or wizard was aware, a player doing multiclassification as another class could use it to cast a spell of that other class, such as a multi-class wizard-paladin who could choose in the list of paladins despite paladins could they not adapt otherwise?