The short-term fund has tracked closer to the underlying index than the medium-term fund has. Well-regarded options-market blogger Adam Warner from Daily Options noted that the VIX generally has a negative 0.66 correlation to the S&P 500, and the Short Term Futures ETN captures 40% to 50% of that effect. He notes that there are no enormous flaws in the VIX ETNs such as those that have surfaced in other exchange traded products. However, a possible obstacle could be a negative roll yield, which would occur if, in rolling to the next month's futures contract, the fund has to pay out more to buy the new month than was taken in by selling the old month. That has been a huge obstacle for oil ETFs. One aspect of considering new investment products is they need time to prove themselves. Before I would consider using these, I would want to see whether they move up as the stock market goes down. In their short history, the stock market has been almost a one-way trade higher and VIX has gone lower. While there are no absolutes, the funds need to prove they can be a hedge in a down market. For now, the data are insufficient.