It is not just speed- but that is the easiest one to notice. The balance accuracy, adjustability, ability to save and name charge profiles, ability to export charge settings to a micro SD, ability to calibrate the charge voltage, adjustable balance threshold, battery recovery settings, regular firmware updates, reasonably high balance/discharge power, availability of warrant or parts if needed, being able to discharge to a discharge bank or external battery. These are some of the features of the iCharger X6 that I appreciate.

The nice thing about using an external power supply is that the power supply will outlast the charger in most cases, and even if you buy and AC/DC charger, having a good DC power supply will usually let your charger operate at higher power (for faster speed, or charging multiple batteries).