OP Do not purchase anything the store actually this goes for anyone. I purchased a pack of 3 items/weapons and two were good for a moment until I got a new weapon for my mage from a special challenge and the gold sword from SP. You will get better weapons the more you play trust me. Play co-op as well sometimes you get more. 3 matches and at the end of each match you can get up to 3 items, it all depends. So in the end you can get up to 9 if you are lucky. Sometimes they are good, sometimes they suck, sometimes you get an accessory but sometimes in co-op I've got premium items.
No need to purchase items, they really aren't that good and the ones you get randomly or through these challenges are much better.
"And then there's Trevor... the less said about him, the better."