These have made my yoga ball chair usable. The marketing information says these will help short people use the yoga ball chair, but in my experience they are necessary to use it at all, and I'm 5'7" (not short). I bought the yoga ball chair and waited too long to try it out. By the time I found out it was too low to use with my desk, it was past the time I could return it. I was going to sell it or give it away or see if a larger yoga ball might solve the problem. When I was shopping for the larger ball, I came across these leg extenders so I bought them. Now the ball puts me at just the right height to work at my desk. My back feels much better from using this for working at my desk, but I have noticed that the nerves in my butt tend to get tingly when I've been sitting for a while (like the "going to sleep" feeling you get in your arm when you fall asleep on it), and this never happened when I was using my piano bench to work at my desk. It's not a big deal, and it can actually remind me to get up and walk around, but it's a little weird. Anyway, I'm just glad I'm able to use the yoga ball chair at all with these extenders.

I wish the chair would just charge a few bucks more, and come with these.
FYI: You cannot use the Gaiam ball Chair without these if you plan to use it at a desk or even table for work!!!!!!!!! I am an average height of 5'5" and sit at a regular desk and table for work in office and at home - and was forced to spend the money for both sets for both chairs just to have them be suitable for the use the chairs are intended for.

They serve the purpose, but for an additional $15, it seems to be just a money maker for the company. I had no choice but to buy them for my chair at work, and for my chair at home now... so spending $30 JUST to make the chair workable for the purpose it was meant for bothers me.

They are easy to install, and work properly (expect on both sets, the BRAKES seem to enact on their own ALL the time, and it makes me crazy to hear the brake noise and not be able to move). So it seems, the lever for the brakes is not secure and moves easily on its own. So be cautious of that if you have to roll around or slide back and forth at your desk.

Exactly what the chair needed for office use. My knees do not have to bend so much now.

It is perfect for making the chair the perfect height

These extensions are nice. Need to be stackable so i could sit up a bit higher. Overall, nothing bad to say.