made it a singleton

MGStoreKit.h

@@ -14,6 +14,8 @@ typedef void (^PurchaseCallback)(NSString *productId);
 @interface MGStoreKit : NSObject
         <SKProductsRequestDelegate, SKPaymentTransactionObserver>
 
++ (MGStoreKit *)store;
+
 // fetch products data
 - (void)requestProductsData:(NSSet *)products
                    callback:(ProductsCallback)callback;
@@ -25,6 +27,8 @@ typedef void (^PurchaseCallback)(NSString *productId);
 - (void)purchaseProduct:(NSString *)productId
                 success:(PurchaseCallback)callback
                  failed:(PurchaseCallback)failed;
+
+// restore previous purchases
 - (void)restore:(ProductsCallback)callback;
 
 @property (nonatomic, retain) NSMutableDictionary *cachedProducts;

MGStoreKit.m

@@ -19,16 +19,26 @@ @interface MGStoreKit ()
 
 @implementation MGStoreKit
 
+static MGStoreKit *singleton;
+
 @synthesize cachedProducts, productsRequest;
 @synthesize productsCallback, purchaseCallback, failedCallback, restoreCallback;
 
++ (void)initialize {
+    singleton = [[MGStoreKit alloc] init];
+}
+
 - (id)init {
     self = [super init];
     self.cachedProducts = [NSMutableDictionary dictionary];
     [[SKPaymentQueue defaultQueue] addTransactionObserver:self];
     return self;
 }
 
++ (MGStoreKit *)store {
+    return singleton;
+}
+
 - (void)requestProductsData:(NSSet *)keys
                    callback:(ProductsCallback)callback {
     BOOL haveAllCached = YES;
@@ -49,7 +59,9 @@ - (void)requestProductsData:(NSSet *)keys
     self.productsRequest =
             [[SKProductsRequest alloc] initWithProductIdentifiers:keys];
     self.productsRequest.delegate = self;
-    [self.productsRequest start];
+    dispatch_async(dispatch_get_global_queue(0, 0), ^{
+        [self.productsRequest start];
+    });
 }
 
 - (BOOL)canMakePayments {