(Bloomberg) A number of hedge fund firms have a hot product. It’s not their hedge funds. Och-Ziff Capital Management’s investors withdrew $418 million from its hedge funds in the second quarter. Total inflow of assets under management, however, were $1.2 billion, its largest increase in assets in four years. The firm’s hot product: Collateralized loan obligations — a derivative debt investment that invests in leveraged loans and is a cousin of the type of funds that blew up in the housing bubble.