Not sure of difference, but the CSA receivers imported into the US are the single stack versions of the receiver. Corwin, when selling this safety selector, said it only works the CZ858 (b/c built on full auto receiver at the CZ factory) or US receivers only w/ full auto specs...
Looking at pictures, the NEA safety has a narrow slot to the left that the the Corwin's selector doesn't. Maybe the receiver differences result in a different trigger pack setup/alignment?
EDIT: Corwin does have that narrow left slot, but at top only. Pictured is bottom view. Looks like the difference is that wide middle on the NEA that I verified the Corwin doesn't have.
Corwin:
NEA: