I kind of think given the large amount of time required to get currency (especially since it isn’t really skill based) you should at least only unlock cards for people you own. This is doubly true for when you spend actual money on cases. Nothing like dropping $20 on elite cases only to get 4 silvers and a gold, none of which you can use without spending additional money… (or grinding forever)
At any rate, I opened 15 normal cases, and got OK cards. Couldn’t use any though. ¯_(ツ)_/¯