What's the biggest difference between this and a regular tablet running linux (I'm not sure they exist but I'm assuming most android tablets can run any Linux?). Is it the addition of GPIO, or somethinbg else?
This is definitely not the case. There are almost no android tablets that people have even bothered figuring out how to boot normal linux on, and I'm not sure there are ANY that have complete driver support.
Other than this your best bet would probably be to try to find an x86 tablet from 5 years ago and even those are a huge pain to use linux on.
1) you have access to the Raspbian and Pi ecosystem 2) it has actual usable UI, commercial-grade I would say
The whole idea of this project is to help makers to be portable with their projects. The display is optional.