This is a great exercise ball.  I bought it to replace my chair at work.  I love that I can sit on it comfortably all day and that it supports my bum and encourages good posture.  My abs are getting a little work-out also.  The instructions were easy to follow.  I pumped it up with a Shrader bike pump, so there was no need to purchase an additional pump.  I've only had it a few days, but so far no deflation whatsoever.  Several people at work told me they're now thinking about getting one.  And I just bought another one for my husband.  I am 5'5" and bought the 65CM size.  I think the 55CM size might have also worked okay, but I prefer this bigger size.