I bought this in order to improve my finger strengh and independance for playing guitar. I had thought of buying one years ago, but my view was - if you want to improve your finger strength and dexterity for guitar, just play guitar, right?
But I changed my mind, and decided to give this little device a go, on the grounds that I can use it when I'm NOT able to play guitar (like when I'm at work) and maybe using a device with some resistance might accelerate my finger strengh gains?
This is a pleasingly well made unit, and the plastic parts seem to be of high-quality. I decided to go for the red "medium" excerciser, having read some comments here about more reps and lower tension being more beneficial for musicians.
When the unit arrived, I was beginning to think I should have gone for the 5lb device instead! The tension initially felt quite strong, particularly on the little finger!
Well does it work? in my opinion definitely yes! Having used this device for only about 15 mins a day most days for 3 weeks, I suddenly find that the spring tension feels a lot lower. Also it has transformed my guitar playing! Playing my 12 string acoustic guitar suddenly seems easier, and on my electric, hammers and pulls seem much more accurate and clearer! my speed has improved, and I recently found myself doing vibrato with my little finger, something I don't normally do!
So yes, I think it works for Guitarists (and other musicians) and it's quality means that it is good value for the money!