So the e-ink display consumes power only when the picture is changing. (e-ink-reader.ru)
The main bonus, however, is power saving, as the e-ink display only consumes power when changing what's being displayed, and there's obviously no need to generate light either. (androidcentral.com)
Bluetooth 4.0 ensures the tracker sends data to any device of your choice without consuming power from the battery. (fussy.org)