Huawei is pushing for a new memory card standard NM but is it any good? Benchmarks show that the cards perform on par with their microSD counterparts. They use the eMMC 4.5 protocol with an UHS-I U3 speed rating, promising peak read speeds of 90MB/s and sustained write speeds of 30MB/s.
Thats theoretical, heres what you can expect in practice based on the numbers by Hi-Tech:
Copying a 6.7GB file took 1 minute 33 seconds, thats 72MB/s. Note that a 128GB NM card was tested (user-available capacity is 123.73GB after formatting). Currently thats the only capacity available, but 256GB and 64GB models are coming (all manufactured by Toshiba for now).
NM card storage benchmark
Only four phones support the standard, the four Mate 20 models, though there are probably more on the way. Theres a USB adapter if you want to browse one of these cards on your computer, but they are not nearly as ubiquitous as SD readers.
Source (in Russian)