Are you sure it was the .223 version to played with and not the cheaper .22? Most polymer and plastic rifles have the cheap feeling in my opinion. But that doesn't mean they cant be durable. As for it being clumsy, I guess it comes down to personal preference, experience and ergonomics. With that being said, the Beretta ARX is obviously durable and ergonomic enough t a degree to serve as front line rifle for the Italians and others.
MAC did a initial hands on video about the Beretta ARX. His follow up review video is nowhere to be scene. He also did a video regarding the alleged magazine compatibility issues.