I use TDUK Cache Cleaner but it only works on firesticks using version 7 Amazon operating system. I tried SD Maid but it did not work with my firestick.
I have not tried it on a Fire TV Cube. However, it should work on any Amazon device using version 7 of the operating system. I have it working on both my firestick 4k max and also on my JVC Fire TV.
Background apps only does what you can do yourself by going into settings> application> manage installed application>force close any app> clear cache.
Defsquid>Manage Apps does the same thing. Remember, do not clear Data or all your app settings and logins will be removed and need to be reentered. Cache is only a major concern if you are short on storage otherwise I only clear the cache every night before I power my device off. Best performance boost imho is Fast Task Killer in Troy’s RAI.