The industry's first 128 GB ultra-fast UFS 2.0 embedded memory for next-gen high-end smartphones has just entered mass production.
http://www.notebookcheck.net/Samsung-intros-128-GB-UFS-2-0-embedded-memory-for-smartphones.137249.0.html
eMMC is just with semi-duplex mode on the read and write, so there often get stuck.
UFS and SSD support the full-duplex of the read and write, that are absolute much more smoother.
(You must be careful, some profiteers claimed of the "SSD" actually was eMMC inside the device, deliberately did not indicate the eMMC, especially for the tablets and inexpensive 2-in-1 hybrid-books)
That SSD claim usually happens with very cheap Chinese devices. Obviously, most of the time it's about no-name ones sold on DX.com. AliBaba and other similar websites.