Three of the last 6 cartridges (different materials) I purchased had a bite valve without a slit. I tried pushing the valve until the cows came home but it did nothing. In the end, I made a slit with a scalpel, and they have worked fine ever since. I also check that they valve is firmly attached and regularly monitor the prints.
I personally have suffered at least three spills over the last year from different causes, but Formlabs has always taken care of it via the service plan. Most of my spills come from prints tearing off, then sticking to the tank, and causing the wiper to flick resin out of the tank. Only one case was it a straight overfill where the printer just kept dispensing resin for some reason.
I can’t image owning one or more of these printers without the service plan. Trying to clean them up after a severe spill is a royal PITA and causes excessive downtime. Even a minor wiper splat spill makes a holy mess, takes hours to open the printer and clean, and makes me nervous as a cat around water with each print afterwards.
IMO, the tanks should be able to hold the entire cartridge, or the printer should have a drain system to catch overflow into a bottle, or the cartridge should be redesigned to prevent these types of mishaps with a mechanical valve.