This article sheds some light on how these double leveraged ETF’s and ETN’s work.  After having a bad experience with (TBT) which is the ultra-short 20 year treasury ETF, I will never use one of these again.  It really comes down to knowing exactly what you are buying, and due to the way that these are structured, it just isn’t something I am comfortable with.

http://finance.yahoo.com/blogs/breakout/warning-investors-don-t-tvix-ed-says-macke-162642044.html

INVESTING IN THE FINANCIAL MARKETS INVOLVES RISKS. OPTIONS ARE NOT SUITABLE FOR ALL INVESTORS.