Reminds me of the Minolta catadioptric, 250mm, F5,6. It was, when they discontinued it, dirt cheap (about Euro200 equivalent). Nowadays, you can find used ones for Euro1500...
And, an f/5.6 mirror lens lets in only about as much light as an f/8 refractive lens.
The challenge for cats in everyday work is the vanishingly thin DOF. They can be decently sharp (in theory even sharper than a refractor) at the exact point of focus, but the lack of central illumination causes a more rapid loss of sharpness as you move away from perfect focus. That feature makes them more challenging to find focus with as well. They also have a pretty severe loss of MTF at medium frequencies (that gets worse at lower f numbers) and that causes loss of contrast that has to be fixed in post. I have 10 different cats and love to experiment with them, but they are not suitable for everyday picture taking other than, as you suggest, possibly Astro, where mid frequencies are not of interest when looking at points of light and there truly is only one point of focus, infinity.
