Ok starting from the top...
A non-venting SS DIN plug used in a high fO2 environment is not a great idea. The plug actually damages the threads in the DIN fitting because there is a ****load of friction if there is pressure behind it - hence needing a big wrench to undo it. Is that risk more or less than venting an AL40 of O2 into your car? Hard to say, neither happens often enough to develop a risk profile.
The venting plug is not "o2 cleaned" and DGX doesn't want to vouch for those convoluted passages being "o2 safe" BUT they mostly mitigate the high pressure O2 locking the plug into the valve if the knob gets bumped. You may still need a wrench and light force to remove it because the oring gets wedged into the sealing surface. But no massive friction forces involved.
DIN fill whips are fully vented prior to removing, and the DIN fitting itself provides enough leverage to remove it (moreso than the plug) hence you never need a wrench to remove these unless that valve is really corroded.
The mass of O2 behind a DIN plug is quite small and there has never been a publicized DIN plug O2 fire. There have been fires from accidentally turning on O2 tanks abruptly. Also fires from trying to remove a valve from an O2 tank while pressurized. Make of that what you will.
PS the Delrin and plastic plugs are awful. Yes they have a vent hole "in theory". They can and have shattered when pressurized sending grenade like plastic fragments into a diver's hand more than once because the hole is too small or the material too weak or the pressure is too high or all of the above. Either use a SS plug (venting or not as you see fit) or don't use a plug at all.
