Should I buy and hold volatility-linked ETPs?
In general, no. Volatility-linked exchange-traded products oscillate around an average value in the short term, and tend to be mean-reverting in the long term. That makes these products inappropriate for buy-and-hold investors. Furthermore, the prevailing term structure present in VIX futures (contango) generates meaningful performance drag if volatility-linked ETPs are held for long periods of time.
FINRA put out in October of 2017 (http://www.finra.org/industry/notices/17-32) on long-volatility tracking ETPs, which is well worth reading. Here's a salient excerpt:
"Because of the negative roll yield, many volatility-linked ETPs that seek to maintain a continuous, targeted maturity exposure to VIX futures, particularly to shorter maturities, have lost a significant amount of value over time; ... The risks of volatility-linked ETPs have been highlighted by both academic and financial publications6 and firms, registered representatives, their supervisors and investors should understand the risks of these products."
Inverse ETPs, or those that include volatility as part of a broader investment strategy, may be appropriate for some investors over longer time horizons, however each of those strategies is unique, and will require due diligence on the part of any investor.