Charging speed of each device is based on the rate of charge the manufacturer will allow into the battery. Each device is different. For example, the iPhone 6 includes a 5W charger in the box, allowing about 1A charging rate. But, Apple actually allows you to use 2.1A charging rate max, which of course is faster.
Reeljuice's max charging rate is 2.1A, which is typically the fastest charging rate allowed by phone developers.