I have tried one but I think its a bit too expensive for what you get. It does work but I found it a bit too fiddly to alter and that when playing hard the capo had a tendency to work loose causing some weird sounds. Its really just a gimmick and I think that it would be better to learn to tune your guitar in various tunings. I tend to use more than one instrument so one is always in standard tuning.
Good luck
Pete