step up packs are a gamble...i've personally seen allies open 400-600usd without any 6star.
some spent 400 and got alexander the troll 6star.
even at step 7, chances is still just 2% to get any random 6star. it's very possible to get zero 6stars even u open 10 packs.
if you want to gamble, go ahead, if you want to get THE EXACT 6 star you WANT,just buy with with TE.