My experience with a 128K years ago is that it was difficult to find *anything* that will run on it, much less frivolous things like a screensaver. There is really zero room to run anything but the application you are currently using, I agree, just turn down the brightness knob or shut down the machine. It's not often that you see an old Mac with serious screen burn anyway. The few worn out tubes I've encountered in them were simply weak, worn out gun, and a screensaver does little to prevent that since the gun is still being used to display the screensaver, albeit generally at a lower average beam current.