Is using a Fire Extinguisher for injected CO2 more dangerous?

[FrozenShivers]

Hello, making this thread as the discussion started elsewhere and started to derail another thread. Some people say that using fire extinguishers in an aquarium setup can have added risk as opposed to normal cylinders due to them not being used for their intended purpose, this makes sense to me. However, the reality is that there are thousands of people using fire extinguishers to inject CO2 and it has been happening for years without regular failures due to them being fire extinguishers. This doesn't mean that they aren't more dangerous than standard cylinders for our use. Do fire extinguishers fail more often? Are their failures more catastrophic? Both of the aforementioned or neither? It could be that they are only very slightly less safe to the point that it's well within the realms of acceptable risk that most of us are happy to have in our day to day lives.

 

[Little]

I tried to research to understand the difference between a FE, Soda Stream, Paintball, Food Grade, Mechanic and Aquarium specific canisters. As in, how are they physically different from each other.
Aside from attachment fittings, It seems the main differences are the canister size and weight in relation to the volume of CO2.
This suggests they carry CO2 under different pressures and / or have different thickness of steel or materials used.

I suppose the regulator likely plays the largest part in safety. Perhaps a cheap regulator on a large high pressure vessel could potentially have a higher risk of discharging all the CO2. It’s all just an assumption.

Another safety factor could be large canisters potentially going long periods of time without being assessed for signs of faults. I read about fire extinguishers on ships that rust (damp salty air on painted steel canisters).

I personally have a preference for being risk averse so a smaller canister under lower pressure that can be refilled or replaced regularly gives me a feeling of safely. Additionally a regular from a known brand whom is more likely to quality check to safeguard their brands image.
This could be totally unnecessary and brings a higher cost and time commitment.