But outside of black-swan events, you are going to lose money investing in such a fund. It is more like an insurance policy than a traditional investment.
Traditional investors might hold lots of equities during a bull market and fewer equities during a bear market. A fund like this allows you to maintain a more constant percentage of equities, with the understanding that you're spreading your losses over time, instead of incurring more significant losses during a sharp market downturn.
Similarly, you can make some excellent money in a 3x bear fund if your trades are fortuitously timed, since they aim to give you three times the amount their associated index loses in a day. But it is not a buy-and-hold investment. If you buy and hold, your money will eventually disappear.