Product review (2 stars): Twist & Shout
Last year I bought this as my annual replacement filter for a Whirlpool refrigerator. I was pleased to find it on Amazon since it was considerably cheaper than the factory recommended version. As a bonus it was "green".  Installment was easy, though conditioning the filter medium was necessary. Basically, all you have to do is follow the instructions and it works out fine. So the filter performed as well as the factory version over the past year.  Flavor was great and no particulate matter showed up at any time.  When it came time to replace it, I figured I might as well get another one. I went to my Amazon orders page and found the orginal order and bought another, knowing I had ordered the exact same product. The filter showed up a few days ago; I handled it the same as the one from last year but when it came time to hook it up to the refrigerator it wouldn't fit. I tried several more times but it still wouldn't go on. I double checked the model.... all the same as it should be. Finally I took a very close look at the small collar in the center of the filter and found that it sat fractionally higher than the older filter. This prevented the locking lugs from engaging while attempting to do the "twist-on".  While I was using up my more seasoned vocabulary of expletives during this procedure I recalled some of the negative older reviews by Amazon buyers...... many of them were because they couldn't get it to fit,  too.
  Can't recommend this product as there apparently is a problem with quality control at the factory.  Many buyers have been happy, as I was this past year.  Those reviewers who couldn't get it to fit tell another story. To Amazon's great credit, they make it as easy as possible to return a defective product and I will have a refund.