XIV sure seems to behave a lot like long Vix futures calendar spreads. When the vix goes down, XIV goes up and long Vix futures calendar spread (short front month, long back month), also go up, etc. What are the differences in the two devices, and the pros and cons of one over another? I have been using them interchangeably over some months and often have trouble deciding which one to use to express a bearish view on volatility. I would think the spread would be more resilient in the face of major volatility spikes, being a hedge and more of a increasing contango play than an outright bearish bet on volatility, but then they seem to behave so similarly. Any thoughts?