I bought this J Fit a few months ago from Amazon because I was looking for 45cm size ball for my kids. I already have 55cm size my kids use which is a different brand (Everlast).
Upon receiving the J Fit and using the product I was immediately disappointed. For starters, the pump had stripped threads so I was not able to use it...luckily I still had my Everlast pump. After I pumped up the J Fit ball I noticed it was clearly lopsided even though I did not fully inflate. I played around with it by putting more air and less air and it was lopsided in all scenarios. The actual material doesn't feel as rugged as my Everlast ball.
On the positive side, I've had the J Fit for several months now and it has not popped. But overall I have to give this J Fit 2 stars based upon defective pump right out of the box and lopsided ball. I would not purchase this brand/model again.