Maximum airspeed wether expressed in knots or mach are still the same.Its just another way of describing maximum certified airspeed on. As for Vmo this is also the truth.
You should not however confuse this with "Coffin corner" or (Mach crit) as we are not talking about this. Vmo=Vso
U know with higer altitude the IAS is dropping thus TAS is increasing. therfor the barber pole is going anticlockwise.Showing
maximum IAS which correspond to Vmo.
And not to forget that Beech is trying to sell themselfes with mach numbers in the specs rather than TAS. The sound of it is better I would imagine.