To add to this, the main reason the Anker device charged faster is because the Anker device supports Power Delivery over Type-C, while the Naztech only supports 15W max over Type-C.
So the Anker charged at twice the rate because its PD spec supports up to 20V/1.5A, or 30W, literally double the speed of the Naztech.
What you need to consider in the end here is what you really need a power bank for. If you have a ton of 2-3 generation old cellphones and USB devices, you might want this Naztech power bank instead because it supports Quick Charge 3.0 where the Anker you mentioned doesn't. If you have current-gen Type-C smartphones, a Macbook, or something like a Nintendo Switch, buying a power bank that supports Power Delivery will benefit you equally or greater over this. (Or alternatively, you could shell out a bit more money and get a power bank with both QC3.0 and PD so you have both options available)
For example, my LG V30 supports both QC3.0 and PD, and charges at the same 18W rate on both, so it makes no difference to me which bank I use. My Nintendo Switch can make use of PD though and charge faster. So in the end, a PD device is better suited for me.
Just things for everyone to think about!