Have you ever done the maths on how much more air is in a 300bar ?
1bar = 1volume, so assuming a 12ltr cyl, the 232bar contains 2784ltrs of air, a 300bar 3600ltrs,
airguns need to be refilled at around 120-140bar but as the cyl empties you will only equalise the pressure between cyl & rifle, so between 1440-1680 ltrs of that air in effect cannot be used, because it's under 120-140bar.
So in practical terms a 232bar 12ltr contains between 1104-1340ltrs of useable air, a 300bar 12ltr contains 1920-2160ltrs
that's a lot more fill's/top up's.
caveat;
That is theory, air at pressure is funny so the figures don't actually work out exactly.