Here's my presentation on the Masterplay Interface Clone for the 5200 complete with newly gleaned info on using a trakball on almost any and every 5200 title in the library. I got unexpectedly great results on games like Defender, Ballblazer, and Gyruss.
I also show how to use everything from Master System joysticks to NES gamepads to Playstation 2 flight sticks on your 5200.
https://m.youtube.com/watch?v=x7qcW_8Fb4Y