Why do you want one? I've never used an Android TV box, so don't know what version (or perversion) of Android they might run, but in general task killers are a bad idea on Android, messing with the OS's optimisation and wasting more power than they save, all in the aim of keeping RAM empty which is itself a bad way to run any operating system (except possibly Windows, since MS have never been very good at memory management, and even then I'm not sure about current versions). Of course these things are all programmed to tell you what a wonderful job they do, but anyone can write code that tells you it is doing something useful. But unless Android TV boxes are very different from other Android devices I'd personally not install anything that claims to be a task killer/RAM booster/system optimiser/any of the other names these bits of snake oil go under.
