Anyone have experience using these? I have noticed that my ring and pinky finger are weak when playing guitar, almost to the point where my pinky is unusable on the top 2 strings. Also, what strength do you recommend?
Just set some time aside in your practice to focus on your ring and pinky strength, it will come im time. Just play something you would normally play with your first two fingers, but use your ring and pinky instead.
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Nothing will strengthen your guitar playing quite like playing your guitar.
Quote by Altered_Carbon
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I, like everyone else recommend practicing as well.

Doing hammer on and pull of techniques properly is the absolute best practice for strengthening your fingers.

If you insist on a portable guitar practice tool, the shredneck would probably be a better option. I don't see how it can help too much, but I guess it beats not playing guitar at all.
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If today's work is hard, think future, each day the stuff you'll do will just be easier & stronger, stop hiding behind technology & come play with the hard stuff. Especially since your ring finger is your best bending tool, its pushing angle is just the best for bending that G string up to the edge of the fretboard, that'S right, push these ****ers.

Try putting bigger gauge strings on one of your guitars, when you'll pick up the other you'll think you'll be playing butter. I put .12-.52 on my LP tuned to D, that'S approx acoustic tension, so that I can play like a bitch on E on my Eb fat strat with .11s on it. And even tough it'S easier (as much as light strings without hand training) the stronger strings will actually last longer & allow for a better vibrato control, better sustain, wider dynamic range etc etc we know the drill.

Good luck I kinda sympathized for your cause.
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I've got one, and it's like it advertises, a Gripmaster ...It's more effective for something like rockclimbing where you'd need massive forearms to grip ledges, as far as (applicable) strength or speed in the fingers, I didn't notice an improvment.