I hate MOST of them. I use them at work because that's the only way we have to organize them. The management hates it when we spend money on tools. Maybe I'll make a better organizer out of wood when I get a chance. The most used sockets aren't on rails though, they are in a blow molded case.
For my personal stuff, I have rails that came with the sets. The plastic ones are okay as the socket is usually retained well and not too difficult to get on/off. I plan to make organizers, but I rarely work out of my toolbox at home so it isn't an issue.
The only reason I'd get them is for a portable tool box. And at that, I'll only get the plastic ones.
I got some Ernst rails with my SK metric set, and they are nice. I don't trust them for durability though as some of the clips were broken during shipping. I still would prefer a quicker way to access my sockets though.