I’m Chinese so my English is not very well, but I hope my solution can help you improve the speed of ssd .
Before I bought this tablet, I found some information about core M3-8100y. Intel just tell me it supports pcie3.0 with 10 lanes, there is no more information able its SATA controller. But for N4100,it also support SATA3.
When I search the review and benchmark of CHUWEI UBOOK PRO N4100&M3,it seems like their SATA Controller all work at SATA2@3Gbps.It’s very strange because using sata2 can not save any cost for CHUWEI.
By a chance, I entered the BIOS and got it——the reason why they work at sata2 is SATA Controller Speed is set as gen2.
Just reboot your tablet and press Esc to enter BIOS, then switch gen2 to gen3.Now your ssd can run double speed than before.
As for the socket of ubook pro m3, it seems like a M.2 with m key for UBOOK PRO M3,because I saw NVMe information in BIOS; N4100 don’t support pcie3, so I assume it uses a b key socket,
you can try to switch SATA Controller to gen3(if there have this setting), and if you want to upgrade ssd, please buy a M.2 SATA SSD.