They provide good transfer rates considering its diminutive size
Together with the Mate 20 series, Huawei introduced a new memory card format called NM cards. Sporting the same size as a NanoSIM, NM cards aim to make memory cards smaller while providing roughly the same transfer speeds of a MicroSD card. The NM cards available in the market right now claim up to 90mb/s read speeds. To see if the claims are true, a Russian blogger ran benchmarks to an NM card and the results are quite impressive.
Based on the benchmark tests, the NM card can do maximum read and write speeds of 74mb/s and 83mb/s respectively, with average read and write speeds at 70mb/s and 73mb/s. What makes the NM card impressive is its high write speeds. For reference, the HyperX MicroSD card we reviewed gave us read and write speeds of 78.82mb/s and 37.97mb/s.
Right now, only the Mate 20 series support NM cards, and they have a steep price. We hope Huawei pushes through in making NM cards accepted by other mobile brands, as NM cards appear to be promising in providing decent transfer rates while keeping a smaller physical footprint.