I've got a couple of those I found on a 3 pin bracket that came off a house. One's got the CP logo, the other is unmarked. I don't think they're that common, but it's tough to be sure, not a lot of dedicated mud collectors up here. They're the only ones I've seen in 10 years of collecting.
Hi All: I have it on good authority that of the 3 colors this piece comes in, the brown is the most common. There is an ugly dark brown and a white version also found occasionally. Any of these are rare in porcelain circles. If it were glass, it would be like a 718 ... if you know what I mean. Since they rarely change hands, a value would have to be what-ever the buyer and seller work out.
Thanks for the good news Robin. I'm thinking of an entire sub-collection of CP pieces. They had some nice designs and glazing. I have a bunch in storage out at the cabin,,, time to clean them up!