I think any of these future ETFs likely lose money over time. They shouldn't be held forever, otherwise you're just paying theta to the banks.
I mean look at the VIX options, if you were long VXY in October 2011, it'd be worth essentially 0. If you went short (SVXY) the VIX, you'd only be up 30% and that is assuming you didn't get stomped out during the blowup last year. Not sure if that impacted the return, just looked at the SVXY chart but these instruments weren't meant to be held and are pretty much sucker bets for retail investors.