Trout,
A couple of drawbacks with comm ETF's is roll yield, and daily re-balancing against the underlying.
Fund Summary
The investment seeks to have the daily changes in percentage terms of the Shares’ NAV reflect the daily changes in percentage terms of a weighted average of the closing settlement prices for three futures contracts for corn The fund normally invests in Benchmark Component Futures Contracts or, in certain circumstances, in other Corn Futures Contracts traded on the CBOT or on foreign exchanges. In addition, it also may invest in exchange-traded options on Corn Futures Contracts and in corn-based swap agreements that are cleared through the CBOT or its affiliated provider of clearing services in furtherance of the fund's investment objective.