First off, let me say they are not perfect. I have on occasion had the issue of plates getting stuck and having to readjust the cradle, which is exacerbated if your floor is not perfectly level.
That said I'm still giving them five stars because I just love these things. They feel better than any dumbbell I've ever used with fantastic knurling, are extremely compact, and the sliding mechanism just is extremely satisfying. Personally, I don't find the rails to be an issue and I actually like using them as a grip for French press and pullovers.
As a tip, you can use the power block powermax stand for them, which includes a way to hold the adder weights as a cheaper alternative to the Rep stand when you find them on sale.
Performance
Value
Build Quality