GetAllDetectorData() and GetAllDetectorDataSafe() are both methods that can be used to retrieve detector data for a specified detector object. 

1. The main difference between the two methods is that GetAllDetectorDataSafe() returns a two-dimensional array of double values double[,] that contains all the detector data for the detector object, while GetAllDetectorData() returns a boolean value that indicates whether the detector data was retrieved successfully, and one-dimensional array double[] .
2. GetAllDetectorDataSafe() does not require the input of numPixels and detectorData, whereas GetAllDetectorData() requires these parameters in addition to (detector) ObjectNumber and Data(type).

Check the examples to use the two methods: 

For python: 

TheNCE = TheSystem.NCE
DetObj = 4
obj = TheSystem.NCE.GetObjectAt(DetObj);
numXPixels = obj.ObjectData.NumberXPixels;
numYPixels = obj.ObjectData.NumberYPixels;

DetRectangleData_FluxArea = TheSystem.NCE.GetAllDetectorDataSafe(4, 1)
for x in range(numXPixels):
    for y in range(numYPixels):
        print(DetRectangleData_FluxArea[x,y])

numPixels=numXPixels*numYPixels
detectorData=np.zeros(numPixels, dtype=np.float64)
bool_value, detectorData= TheNCE.GetAllDetectorData(DetObj, 1, numPixels,detectorData)
for i in range(numPixels):
    print(detectorData[i])

For matlab: 

TheNCE = TheSystem.NCE;

DetObj = 4;
obj = TheSystem.NCE.GetObjectAt(DetObj);
numXPixels = obj.ObjectData.NumberXPixels;
numYPixels = obj.ObjectData.NumberYPixels;

DetRectangleData_FluxArea = TheSystem.NCE.GetAllDetectorDataSafe(4, 1);
for x = 1:numXPixels
    for y = 1:numYPixels
        disp(DetRectangleData_FluxArea(x,y));
    end
end

numPixels=numXPixels*numYPixels;
detectorData=NET.createArray('System.Double', TheNCE.GetDetectorSize(4));
bool_value=TheSystem.NCE.GetAllDetectorData(DetObj, 1,TheNCE.GetDetectorSize(4),detectorData);
for i = 1:numPixels
    disp(detectorData(i));
end

In matlab, the retrieved data from GetAllDetectorData() need to be rearranged from 1D array to a matrix, detectorData = flipud(rot90(reshape(data.double, rows, cols)));

and here is a simple example to show the transform: