I recently ordered a couple of cheap $185 X98 Air 3G’s for resale and although the Banggood listing said they were Windows 8.1 models, to my surprise both models have Windows 10 preinstalled from the factory. So Teclast stock, at least on Banggood.com is now shipping with Win 10. You can, of course, upgrade your Windows 8.1 X98 to Windows 10. But this version has the recovery as Win 10 which is handy if you want to reset the tablet.
The eMMCs in my two and Toshiba’s and quick for eMMC 4.5.1 units. I got these for $185 from Banggood with coupon 3f3128 if you’re interested in getting the same deal.