Managed to get hold of a Sweet Armor bumper, and did a comparison against the SZLF bumper. These are the main differences I noticed:
1. Difference in color tones. Sweet Armor has more vivid colors, but its surface finishing is slightly dull, thus concealing the 'metallic look'. SZLF has more shine, and its natural color matches closely to the aluminum battery covers. Sweet Armor is a better choice if you prefer a more vibrant tone for certain colors.
2. Sweet Armor weighs 20g. SZLF weighs 18g.
3. The internal lining on Sweet Armor is poorly done and is just some plastic tape stuck on randomly. SZLF is factory-lined with soft felt cloth.
I didn't measure the dimensions, but they appeared to be similar. Port and button cutouts should be quite similar as well. That said, the general look and feel is different, and they are definitely not from the same OEM.