This is a standard UIKit
object. It will appear as it should on each system.
If you don't like the small bar in iOS 7, you should customise it.
You can do so quite easily with UIAppearance
proxy but you'll need to do so with images, pretty simple, just make your images look like iOS 6, and you should get what you expect.
The properties you'll want to customise should be:
@property(nonatomic, retain) UIImage* progressImage NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;
@property(nonatomic, retain) UIImage* trackImage NS_AVAILABLE_IOS(5_0) UI_APPEARANCE_SELECTOR;