Product review (5 stars): EXACTLY the same size as the old filter! NSF 42, NSF 53, and NSF 401 certified.
I almost didn't purchase this filter because there is a highly uprated review saying this filter isn't the same as the old one. But I found it unreasonable a company would manufacture a replacement filter that is a different size than their old one. With Amazon Prime same-day delivery and easy returns, I decided to take a chance.

They are EXACTLY the same size as the Whirlpool 4396508 filter it replaced! It is a PERFECT fit.

The cheaper off-brand clones don't come with NSF 53 or NSF 401 certification. They can only filter up to NSF 42 standards, so you simply won't get the same level of protection against biological contaminants.