I have 2 whisper 3s on a 55 gal, one on a 20g X-high, and a whisper 1 on a 10g.
I like them for having a reusable bag... take it out, hose it down and reinstall it... add charcoal if you want... and when they wear out, order more online for about 50 cents each.....
I also like being able to remove the motor for easy cleaning of the impeller sleeve. The are also low profile and enable me to keep my 55g here on my desk closer to the wall than say emperor 400s.
They do have a habit of stopping from power outages, but I have solved that by using a UPS. (it didnt happen that often)
Also, unlike the emperor 400s, if you throttle down the flow, its not that loud...
Like all filters, their are pros and cons... I like whispers, emperors and wet/dry systems.