We've been using
this model for years. Each unit is supposed to be good for 1000 gallons (I think they say that's a years worth of drinking water for a typical family of 4?).
I've considered trying
one of these, but probably have enough filters stocked up for another 10 years!

I like the idea of being able to see what's "inside" - then again maybe that's not exactly what I really "want" to see?!
I monitor the flow, taste, & check for chlorine removal effectiveness with a little pool kit (which are all reasons to replace the filter). Last time I ordered I got the larger model (green - I think it's at the bottom of the linked page) but haven't replaced the current filter as of yet.
Certainly makes a noticeable difference in taste!!! I can taste chlorine in a microsecond! Makes better coffee for sure...