Phoenix 500mm f/8 mirror lens

Can you tell me how rate Phoenix 500mm f/8 mirror lens is? I rather to hear from you before I can buy the used (look newest) mirror lens on ebay.

Thanks, Eric...

Why mirror lens?
They are fixed aperture, and have ring-shaped out of focus backgrounds.
But they tend to be cheaper, lighter to carry, and of course shorter.

What are most important to you in the lens, size, weight, image quality, low light ability, variable aperture ?