Focus Rail for Macro

[kry10]

I have been watching a series of videos on macro photography, and, the person in the videos recommended a focus rail for the tripod, it looks like a great idea, basically, get focused as best as possible, then, turn the knobs on the rail to change focus.
What is everyone's opinion, useful item, or yet another useless gadget ?

 

[heidfirst]

is your subject going to stay still?

 

[Canon Bob]

They're extremely useful if you're going to use stacked shots to increase the DoF. You can get cheapies from £35 and pay close to £1000 for the bees knees.....somewhere in between is normally of acceptable quality.

Bob