How is the 35/2 Super-Takumar?

[Pentax]

I seem to see a lot more of these than the K or M 35/2's around.

Is it a pretty good lens at the wider apertures?

I've read about something radioactive in the coating which yellows 
but other than that can't find too much on them.

Is the yellowing a problem when shooting black and white or does it 
function like an instant built in filter? I'll probably use it for 
black and white exclusively.

Rob