http://www.styluspick.com/

I picked one of these up from my flatmate. It has some of the hardest exercises ever. I highly recommend every guitarist on this board pick one up or order one today.

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Looks cool, but I might just buy only the picks and sit down with a metronome the old fashioned way.

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Wow, they still make those things? I used those things when they looked like spinning tops. They will REALLY make your alternate picking improve by leaps and bounds. The ones I used, if you messed up, it would catch and you couldn't continue picking. It was a real pain in the ass at first. But it will really consolidate your stokes and make them very accurate.

I didn't use them for very long, but I know it helped by making my picking very perpendicular and shortening the range of motion.

I had the same one Jazadam had, and if anything it made my picking worse. When I would go back to a regular pick, I was like learning to alternative pick for the very first time.

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It's all personal preference. They helped me with my picking style. If you want to be very concise and accurate, I think they will help. If you just go crazy and hit the strings with abandoned fury, they're not for you.