I should point out my poor experience was with Apacer USB drives, not SD cards.
Using my old laptop with USB2 ports I get 17MB/s write speed when writing a 4.1GB image to the Apacer AH356 64GB USB 3.1 Flash Drive stick... $ sudo dd bs=4M if=2018-10-09-raspbian-stretch.img of=/dev/sdb status=progress conv=fsync [sudo] password for ian: 4127195136 bytes (4.1 GB, 3.8 GiB) copied, 239 s, 17.2 MB/s 986+0 records in 986+0 records out 4135583744 bytes (4.1 GB, 3.9 GiB) copied, 241.279 s, 17.1 MB/s Possibly it would write faster if I had USB 3 ports on my laptop. If one goes to the Apacer<https://consumer.apacer.com/eng/content.php?sn=951> website, then their "specification" about their AH356 USB stick is... Transmission at USB 3.1 Gen 1 SuperSpeed Equipped with USB 3.1 Gen 1 interface featuring a 5Gbps bandwidth, AH356 operates at a superlative speed, allowing remarkable read/write speed, making file exchanges between PC and laptop easier than ever. I'm not sure exactly how fast a "remarkable read/write speed" is in MB/s ;-)