Old Tamron Adaptall SP 200-500/5.6 - great or mediocre?

Someone offered me this old, heavy beast, the price is just about 300 Dollars, it looks like new and has an "Adaptall", so I hope I might fit it to my EOS 1v.

There is not much information on the web about this lens, I found this text here:

http://www.adaptall-2.com/lenses/31A.html

It's not the newer 5.6-6.3 lens, no AF, no "DI", "LD" etc.

Had one. Sold it for less than $300 if I remember it was about $225. It was not a bad lens just way too big and heavy. The weight is multiplied by the fact that you also need a heavy tripod to support it. As a result it was never with me when I needed it.
I now use a 100-300mm zoom and a Tamron 500mm mirror lens for long shots.

It should work with your EOS, but you'll have to use stop-down metering; fairly annoying. You'd enjoy it a lot better with a camera that would let it meter at full aperture (e.g. Nikon, Minolta MF, Pentax, Canon MF...).