A Mister uses a more powerful FPGA + ARM CPU board along with extra SDRAM (I believe) to simulate known retro systems.
This was a personal project to make a custom video game console in this case using an FPGA, a couple of years back I finished one using microcontrollers and an actual CPU.
This project uses just enough SRAM and external components and a just enough powerful FPGA to be a retro-styled video game console.
I wanted to learn how to use FGPAs and continue to learn how video game consoles worked while building something unique.
So in a way, in terms of the technology, they're similar, except of course a Mister is something a lot more useful, I would say, as it simulates "real devices" and has a huge game library and this is just an educational project.
Just so you know, the exta SDRAM on MiSTeris only needed for some of the bigger emulated systems (e.g. CPS2). You can emulate a fair number of systems without it.
