You can probably tell from this post that I've never used a rail.
This is my first experience. I had thought about getting one for quite a few years, but always resisted. My new 50mm Z-mount macro has lens focus marking for 1:2, 1:1.4, and 1:1 magnifications. You can manually set it to one of those ratios and use the focusing rail to obtain precise focus. That is what I'm experimenting with now.