One thing - understand that if you elect to purchase any "gems," you are doing so with hard money that will be billed to your credit card through iTunes. It is relatively easy to purchase these gems without knowing you are doing so and without having any idea of the expense. I unknowingly "purchased" 580 gems at a cost of $89.99. iTunes canceled the "purchase" when the scam was discovered but watch out, because it is precisely that - a scam.
This game/app is only out there for one reason - to dupe people into spending money they never intended to spend in the first place. So be careful.