The decay you are talking about applies to ETFs like FAZ. For the type of movements that TBT experiences, the decay is not a significant factor; specially when rates are near zero. If you want sacrifice the bigger upward move for some potential decay than buy TBF. I think TBT will go to at least over 35.
I used to trade it all the time. Usual holding period ranged from an hour to three days. Since so many other stocks have had momentum in the last few weeks, I have found it easier to trade them instead