@seag47 – That's how I would describe them, too. I also saw a photo of an eccentric reducer, and it looked quite different.
Instead of flaring out gradually, it just bulges out suddenly at the side that fits on the end of the larger pipe. It's not a nice, smooth transition.
I just wonder how someone would know whether to use an eccentric or concentric reducer. Is there a difference in the way they conduct the flow, or can you just use either one?