As far as I know radios are required in the US in circumstances where ATC clearance is required. For VFR this means Class D and above. The LAX SFRA is in Class B, which is why the radio is required (as well as a Mode C transponder)
Spiney Norm - you said that the MAN LLR is Class D, which requires ATC clearance for VFR. This would imply radio is mandatory for the LLC - is this true?