Without this product, you will be running back to the store every month or two for a new sized bra during pregnancy, which can get VERY expensive!  This extender is a great value that will save you both time and money.
No, this extender did not make my pre-pregnancy bra last throughout the entire pregnancy.  However, it made each bra I bought last much longer and remain comfortable.  Overall, I only had to change bra sizes a couple of times, and used this in between.  It saved me money and kept me as comfortable as possible.  I highly recommend this product.