Should You Buy ETFs of ETFs?

PowerShares just launched three fund-of-funds ETFs, which means they're ETFs that own other ETFs:

The three are:

• PowerShares Autonomic Growth NFA Global Asset Portfolio (PTO Quote)

• PowerShares Autonomic Balanced Growth NFA Global Asset Portfolio (PAO Quote)

• PowerShares Autonomic Balanced NFA Global Asset Portfolio (PCA Quote)

The names are indistinguishable to me but PTO is the most aggressive at 90% equities and 10% other stuff (combo of fixed income, commodities and currencies). PAO is the middle of the road at 75% equities and 25% other. PCA is the most conservative at 60% equities and 40% other.

The three funds own different mixes of essentially the same ETFs (there are a couple of differences), and track indices recently created by New Frontier Advisors. They all target specific allocations which will be reallocated quarterly, but the prospectus allows for more frequent rebalancing to occur if something truly dramatic happens in the markets like, perhaps, a 1987-like crash. ...