I have used plenty of third party resins. It’s not a “vertical monopoly”.
A vertical monopoly is where a monopolist solely controls a particular device and all other required attachments required for the operation of that device.
As no one else manufacturers cartridges Formlabs is monopolizing in that owns a vertical monopoly.
The key word here is “all” You don’t need a cartridge to operate the machine. You can purchase third party resin and print parts.
The Tank is required but that’s 1 out of 3 for consumables. It’s not a monopoly because Formlabs doesn’t require “all” of the consumables to be produced by Formlabs.
No open mode while forcing the machine to always fill from a cartridge could be a different story.