Clumbers, as a rule, are VERY laid back. They lack the energy of many other spaniels but make up for it with a determination that is awesome. This sounds like a great trait, but be warned, if the Clumber is determined to find or do something that is not what you want it to do or find you need to know what you are doing! A great dog that will look up to a leader but will walk all over anyone else. For the right owner they are fabulous and can be turned onto almost anything that doesn't need it to be fast. For the wrong owner they are aloof, distant and very self interested. They will not run riot - just carry on with their own agenda as if you aren't there.
In an in between household you will end up with a dog that will do what you ask, but it will finish what it is doing first!