Okay, but could be a better design.
As a teaching aid to teach new golfer how to hold the club in the fingers, not in the palm of the hand it works fine.
As a training aid to teach the correct grip pressure, it pretty much stinks. I tried to hit balls with this strip of rubber attached over my glove, as they recommend, and it was not pleasant at all. The edge of the rubber digs into my hand making it painful to use. The rubber strip is so big, it's very uncomfortable to use. It makes the holding a club difficult at best. As for hitting the ball longer and straighter? That's hard to believe as it's so uncomfortable to use I can't see anyone using it for more than a few shots before taking it off.
IF you are a NEW golfer that doesn't know now to properly grip a club in the fingers of your left hand, this might be helpful. As a aid to hitting longer and straighter balls, I doubt anyone would fine it to be of any use. I tried to hit balls with it on, and it was not fun. Hurt the palm of by left hand too much to use it. It takes up so much space inside your hand when holding a club, it's like hitting a club with a grip the size of a baseball bat. I wouldn't recommend it to anyone other than a real beginner, and even then a lesson would be a better choice.