The 5200 mAh battery I ordered was delivered to me for free within two day.
Now, the packaging was excellent and the battery and case were sealed. Having drained the battery once and fully charged it, it has lasted me for more then 2.5x the original 2600mAh battery Samsung provided. I don't know if this is related or if it is simply too soon to tell, but I have noticed that the rate of discharge and also, I have noticed my phone doesn't become as hot as it used to, even when I am using my sat nav (which I do regularly). It is quick charging up, and fits perfectly into the battery slot of the s4.
Few things about the back cover,it is quite slippery, especially to begin with, however, after a while you become used to gripping the phone properly, and I think oil from your hands make it a little easier to grip after a while. Another thing is, I can't find a protective case for the edges of the phone that would fit with the new back cover. However, It is slimmer then I thought it would be (albeit, still quite thick if you are used to the slim original S4 battery). As someone with big hands, it makes the phone a little easier to handle I think, especially if I want to do things with one hand.
Overall, benefits definitely outweigh the cons, and I have recommended this product to many of my friends who are considering upgrading their batteries.