... The Safefill supposedly cannot explode.
Factually that is correct, because you need the correct gas and air mixture to produce an explosion, and a gas cylinder will only contain gas with no air. That applies to all makes of LPG cylinders.
Even if a UK approved cylinder is exposed to extreme heat, the pressure won't cause the cylinder to violently explode, the valve should contain an excess pressure relief device which is designed to vent the excess pressure. The internal pressure will prevent air from getting inside so it should never have an explosive mixture in side.
Even if it did somehow get air and gas inside, the volume of gas and air would probably not have the necessary energy to be able to rupture a properly maintained LPG cylinder.
The risk is mainly when liquid or vapour phase LPG escapes and mixes with air out side the cylinder to achieve an explosive mixture.
Pictures of incidents where cylinders are being hurled through the air are not instigated by an "exploding cylinder", but an explosion outside the cylinder.