That is the reason I have a baking pan under the canister on my fresh tank with a water leak alarm in the pan. I had my fare share of canisters leaking.You stated you have a FX4. I owned FX5 and FX6 which is basically a larger version of the FX4. No way you can tell me cleaning the FX4 is easy. From the media basket to the sponges on the side. The accumulation of detritus on the bottom of the canister. The hassle of carrying the media basket or the canister filter itself to the sink. Where with the filter sock you just have to take it out and place in a new filter sock. Throw the old one in the washer.
Lets not forget the seals fail and you have your entire aquarium on your living room floor. I know that has happened to many people before.