I have two of them, one totally stock, the other hotrodded with f18a DVI video output, a FinalGROM cartridge with the complete cartridge library one SD card, and a whopping 32k sidecar memory upgrade. And homemade joysticks built with Sanwa arcade mechanisms to replace the awful TI ones. Makes PARSEC playable. There are some pretty neat modern homebrew games, too.

https://dnotq.io/f18a/intro.html

https://endlos99.github.io/finalgrom99/

https://thebrewingacademy.com/products/ti-99-4a-32k-external...