iphone power bank are good as long as you are buying a reliable product. The best power banks for iPhone are the ones that are certified to be compatible with the device. You cannot just plug in your iPhone into any power bank that you get your hands on.
An iPhone is a device that is specially curated with much effort and expertise. Therefore, it is important to pick the powerbank for iphone that will not affect its finesse but is wholly compatible with it for a good charging experience.
In addition to the compatibility, you also need to take care of the weight of the power bank. If the power bank is very heavy it will make it difficult to carry it around. You also need to couple it with the right kind of USB data cable.
It is not harmful to operate your phone while you are charging it. Have your selection from the wide variety of approved best power banks for the iPhones.