I think double and triple leveraged ETFs are great, for shorting.
You think a sector is going down? Short the triple leveraged long ETF.
You think a sector is going up? Short the triple leveraged short ETF.
When you do it that way, you gain an edge equal to the fund management and transaction costs plus the inherent losses from the "buy high, sell low" bias in the leveraged ETFs. (when the fund has gains, it needs to buy more at a higher price to maintain its leverage ratio, when it goes down, it has to sell)