The GATCO is a wonderful clamp device that will give you speed and accuracy when you wish to re-profile an edge. It's very well made, has a good selection of stones, and is easy to use.
The primary advantages to using a good clamp device is speed and accuracy. While freehand sharpening skills are desirable, when re-profiling the harder steels used today, the rapid strokes available to the user with a clamp, combined with the absolute accuracy without the need for careful control makes a clamped sharpening finish in 1/4 the time with perfect results.
The disadvantages are to be noted as well. You are limited to just a handful of angle choices. Of course, who really needs more than a handful anyway? There are enough choices to be useful in 99% of the situations.
You do miss out on the 'Zen' of sharpening, but then, that's not really important for everyone.
If your goal is very sharp knives with well-set edges, and get them quickly and easily, go with a GATCO, Lansky, or DMT Aligner and a set of diamond stones.
If you want to experience the Zen of sharpening, or just learn how to sharpen an edge, get a set of Japanese water stones or other bench stones and learn to free-hand.
Stitchawl