I use this external battery for 15 days. I used directly upon receipt without plugging and I've managed to charge my iPhone seven times without external battery is still empty. I therefore reflects the high capacity of this product.
The first small downside for me is the weight for 320 grams in a pocket or a backpack for a hike, it's heavy. The second drawback is that the manufacturer provides a USB cable to charge the product. They could add a power outlet.