I'm pretty sure e-ink has a much higher ceiling for reflectance than TLCDs/RLCDs, so you'll be able to use it comfortably without a frontlight in a lot more situations which could more than make up for increased power usage. I think they are also naturally better in terms of glare compared to any type of LCD.
Viewing angles are also fantastic compared to almost all T/R LCDs - they tend to be fairly directional. It's a great display tech for many things that don't need 60+fps.
And contrast ratio seems far higher to add on to the benefits. I want to like reflective displays, and there are many new ones lately too, but they just fall a bit short, especially if they try to do color
