It was thought that the older ones were too rigid, and this was leading to cracking of the LCA where the tension rod connects. If you dig, you'll find posts on tt.net where people reported this.
I ran them for about 8 years and didn't notice any cracking or visual fatiguing of the LCA. But rather than take chances, I bought the newer style 2-piece that are supposed to be less rigid and installed them a few years ago. No complaints.