All very interesting and thanks for the information. I have a cheap Bay 1 +1 set, "OMAX" for which the thinner piece is marked "Taking." After reading this thread, I tried rolling the viewing lens along and it does indeed appear to have some prismatic component. I don't see a red dot, but it looks as though it wants to be placed so the "OMAX" on the front reads correctly; e.g., right side up. It does appear to have two elements and I see an asymmetrical/tilted line internally, so I guess it's not just sloppy manufacturing.
Thanks,
The ancient and still learning DaveT