Square has made tandem breakers since QO was invented. They make two types. The QOTxxxx which is not a cheater breaker, it can only be installed in a proper CTL (circuit limiting)location. And, the QOxxxx which is only approved for use in existing non-CTL panel spaces that allow tandem breakers (panels prior to the 70's for sure). Use of the QOxxxx in any panel (including NQOD) other than a very old QO loadcenter is cheating.
