They are two totally different animals..The GRE will do trunking and the MarkIII doesn't. The GRE will do digital as the MarkIII to my knowledge does not. The MarkIII is a communications receiver and will scan but the GRE is more geared for scanning systems like LTR,Motorola,Edcas.
I guess it depends what you want to listen for me i do have digital scanners but the intrest to monitor apco 25 signals is not there yet due to mainly monitor the airbands.
I guess it depends what you want to listen for me i do have digital scanners but the intrest to monitor apco 25 signals is not there yet due to mainly monitor the airbands.