I'd just laugh if someone tried to use that in my singlewall metal league, although our league director is a dumb ass & he probably wouldn't know the difference. After all, Mizuno does classify this as a single wall fused metal alloy bat (straight from the source):
"Techfire, Techfire Rage, Fury and Crush are comprised of three different materials bonded together that make up one single wall. Mizuno Triaxial Technology applies carbon and glass reinforced plastics to the interior and exterior of an aluminum alloy. This construction constitutes a single-wall bat. A non-conforming triple-wall bat has three layers separated by air, working independently. The Mizuno Techfire has no air/space between layers. The three materials are bonded and work dependently, therefore, Mizuno Techfire, Techfire Rage, Techfire Fury and Techfire Crush comply with all official tournament standards."
Hell, I'd just bust out a Demarini Aftermath in your league, afterall, it does have a metal handle so it too is not 100% composite!