This is a guide to extract the boot image from a cheap Android tablet based on Allwinner A133 using U-Boot (accessed via UART). With the boot image and Magisk, you can root your Android tablet to make it more useful. An example of a SOC that allows flash reading is Unisoc (formerly Spreadtrum), but on the other hand, the bootloader on phones and tablets with the latest SOCs from Unisoc (that I know of) is not unlockable.