How do the expenses, fees, and liquidity issues factor in? How often can trades be made without these concerns being an issue?
from the CBOE site:
Like many passive indexes, the PUT Index does not take into account significant factors such as transaction costs and taxes and, because of factors such as these, many or most investors should be expected to underperform passive indexes. In the construction of the hypothetical PUT index, the SPX puts are assumed to be written at a certain price on the third Friday of the month. However, there is no guarantee that all investors will be able to sell at this price, and investors attempting to replicate the PUT Index should discuss with their brokers possible timing and liquidity issues. Transaction costs for a put writing strategy such as the PUT could be significantly higher than transaction costs for a passive strategy of investing in Treasury Bills.