I love my Yashicas and I do have one with a Beattie screen which somebody installed before I bought it. I can't say that I would spend that much on a screen for a $100 camera. I have ordered a Satin Snow gg for my Graflex and if it works as well as I believe it will, I will be ordering a few more for the rest of my arsenal of cameras. Stay tuned if I like it you will hear from me. I'm not noted for keeping my mouth shut.
If what you are experiencing is a dark viewing screen, you might want to try cleaning the viewing lens front and rear and also clean the mirror. One of my Yashicamats was owned by a cigar smoker and you wouldn't believe what that did to the inside of that camera.