I personnally flashed various redmi 6/6a with the emmc adapter, and i can tell that those phone come with 3 emmc brands mostly.
1. samsung, this first one always read/write perfectly
2. Skhynix, this one maybe 80% compatibility it has some random write failure.
3. Jmicron, this is the worst, from all i tried maybe 1 connected succesfully.