I asked Don the same question, and he said yes it was relatively rather dim, but focusing was not a problem. And it's less than a stop darker than an Artar which is f:9.
But what I discovered is that for many people, a bright image on the groundglass is the holy grail, even to the point of making focusing more difficult. If you're one of these, you'll likely not be happy with it, as it will be darker than equivalent process lenses and certainly much darker than the f:5.6 plasmats and the f:5.6 400mm Apo Tele-Xenar MRC. Small and bright don't go together, especially in longer focal lengths.
Cheers, Steve