Any screen protector is better than none. If you can't afford (or don't want to buy) a better protector, keep the factory protector on.
You could always use cheap plastic protectors. They work (even on curved screens), they actually give the screen a little more shock protection, and they're cheap.Still have the factory protector on. When it shows more wear than I can take I'll remove it. Naked after that. Just don't like the looks of glass protectors on curved screens.