Some toner cartridge can be easily refilled, some not.
However, even for easy to refill cartridges like Brother, most of the time, users do not know when to stop. They are only will to stop when components are damaged, and toners begin to leak into the printer.
Refilling should be carried out in the factory and with the proper equipment to curb pollution.
On the average,
5/10 DIY toner refillers spill toners at the first refilling attempt.
8/10 DIY refillers will use the cartridge until a lot of toner leaks into the printer.
Toner powders consist of charged particles, plastics, wax, and other chemicals. Inhaling or accidental consumption of toners is detrimental to health.
We have made some models very cheap as we aim to reduce and eventually eliminate DIY toner refills.