Just because IMO the rarity of getting monthly-lockbox-exclusives is a bit much, I think all types of lockboxes should be available on the prize wheel. For example, this month there would be Iron, Mirrored, Titanium, Silver, Steel, and Platinum Lockboxes on the prize wheel. Next month, there would be all of that plus a new one. They would account for 3 slots in the prize wheel RNG: Regular, Mirrored, and Current. Mirrored has its own slot since I assume it has its own rarity value (much higher than normal), and Current is for whichever lockbox is new that month. Normal would be everything from Iron to the one before Current, of course.
Monthly lockboxes are good on their own. It just means that iron lockboxes are going to disappear entirely at this rate.
I would recommend making themed lockboxes and having them drop in the clockworks, and keep the monthly lockboxes on the prize wheel. Already said this more in depth in another thread.