Actually only the oldest of the browns don’t have felt pads. The pads were introduced in 1989 so any browns produced after that date do have them.
And I would have to say that they are relatively common.
But I find that they are very interesting for the evolution of the color over their long production period, and since they’re among the first, you can also see a fair number of variations in the actual scupts. I know there’s a thread somewhere about the variation in eye ridges, forehead and body scales…