Just so there is a proper answer:
Setting the scan options to allow duplicates may degrade overall performance if the CBCentralManager is setup to run on the main queue. It is best to run the CBCentralManager on a separate queue if you need to allow duplicates.
dispatch_queue_t centralQueue = dispatch_queue_create("mycentralqueue", DISPATCH_QUEUE_SERIAL);
_centralManager = [[CBCentralManager alloc]initWithDelegate:self queue:centralQueue];