Nell, The graupners you are getting are certainly more expensive than the stock DJI props but anyone can see the quality difference. I can't understand why people, including DJI, can't see the issue here. These stock props 8" or 10" are simply coming apart in normal unstressed flight conditions and that is dangerous. DJI ought not to be so indifferent over this, these props are randomly failing, that is incontrovertible, just google it. It took three 10" and one 8" blade shear for me to realise there was a pattern and luckily my 450 came down on grass. In the absence of a proper response from DJI, and I've not heard of one, don't worry about the flats on the core, just buy 8mm circular cored blades from another manufacturer.
Looking at my failed, sheared off blades it looks like a tensile break caused by the effect of centrifugal forced. In other words, it could be alleged that the DJI props are under-engineered and are therefore unfit for purpose.