You don't need to pay ££ for them, it's the same as most online games these days..be patient and earn credits etc to pay for random loot, and hope, or hand over your cash and get them all quicker..
Frankly, I don't really know how gaming companies get away with it, it's effectively gambling, creating an addictive environment where with ££ investment, you have x chance of winning something..I mean, I pay, but then I'm a hard working, earning adult.. But exposing young kids to that kind of thing? Poor form in my opinion.