I think that it helps. If you purchase one for a younger girl make sure you get a soft one. My dd complained about it hurting her finger at first but I think that was just because it was different. Now she doesn't complain. It definately helps teach a better grip. We've only had it a few months so when dd doesn't use it she still goes back to her old grip.
I bought a soft one and a hard one a while back. I thought it helped the whole team feel what we talk about with the grip. Some have the feeling down now and others still use it in practice at times.
Most of our girls are small...varying in strength...age 14-17....but overall...they seem to prefer the soft...including me and dd. I like that is gives a little more so they can tell when they are trying to grip with the index finger rather than the grippers.