My experience is that if you can hold your shorting positions forever,
eventually you could short VXX/UVXY etc down. But reality is that your
broker might not let you do it. They will force you to cover before VIX goes
down in a VIX huge-up cycle. So there is still considerable risk associated
with UVXY shorting. Also in many cases, you might not be able to borrow it.
Broker are BLACK, very BLACK.
Buying SVXY might be a better choice. If I understand it correctly, contango
is the dominant trend for VIX futures. Backwardation lasts much less time.
But personally I havenot done any SVXY buying yet. This is only my over-
simplified speculation of SVXY mechanism. SVXY might have time-decay as
other 2X 3X ETFs.
XXV is super and I don't observe any time decay but only premium from
contango for the last couple of years. However, volume for XXV is so low.
Not a very good trading vehicle.