Product review (5 stars): When I was a kid, finding replacement filters was one of life's torments.
I remember my dad looking for a source of various filters (humidifier, dehumidifier, furnace, air conditioner, drinking water) for various appliances with increasing grimness.  The appliance might still be in good shape, but the store that sold it went out of business, and nobody else carried the same line.  Or the manufacturer made some minor tweaks to the design, which just happened to require a different filter, which just happened to make our unit obsolete.  Or it would simply be sold out, and nobody knew exactly when more would arrive.  Dad was a guy who worried, and finding replacement filters provided maybe 5% of his life's quota of worry.

How he would have enjoyed Amazon.  Exactly the right filter, often available from multiple manufacturers, cheap, and delivered within a few days.  Searchable by appliance model number.  Nice clear pictures.  User reviews which point out obscure features and problems.  Every time I order a filter from Amazon, I feel a little burst of thankfulness for the inventors of the Internet and to Jeff Bezos for bringing us Amazon.

This particular filter isn't especially easy to install or well designed, but it's EXACTLY the filter I needed.