even if you get past all the issues that spicymaki mentioned, you'd still run into the issue that most sd cards have absolutely atrocious performance for being

even if you get past all the issues that spicymaki mentioned, you'd still run into the issue that most sd cards have absolutely atrocious performance for being used as something like the boot drive for a computer. even the good micro sd cards are pretty terrible compared to the internal storage in your average smartphone. if using a really slow tablet or phone appeals to you, roll your own tablet with a raspberry pi, touchscreen, battery, and micro sd card.