Contrast is not as good, though can be adjusted though post process. Sharpness wise, may be comparable to tele zoom, but lose out to tele prime lenses. Because of f/6.3-8, it's dark through viewfinder, so only limited to good day light shooting.
mirror lens is smaller in size also (compare with actual lens), easy for carry and transport.
To me, the chance for bringing out a mirror lens is still way higher than long tele lens due to it portability :sweat: