When they say "increased jackpot", they mean they just changed the win rate by .0000001%. It's no use.
It's Nexon logic, you can never tell for sure what they tell us nowadays.
From what i've seen in-game, most people are winning 90 day weapons and a few, permanent guns, so I think it's a good deal. Nexon is obviously making a decent amount of money with these sales since the 30 and 50 quantity cases are good prices. I would never buy it, only because I would rather buy a permanent gun on sale instead, but that's just me.