After recent training with some great espresso people, I'm of the camp that the e-doser is a helpful tool for busy settings, but should not replace basic espresso dosing training.
If someone can learn how to dose evenly and repeatedly with a manual doser, then they have a much better skill-set that they can apply to the handy e-doser.
Also good thing to think about — the e-doser is a timer. You're not getting an exact dose with every grind. You're getting an approximation of an exact dose. A simple change in humidity will REALLY throw you off with an e-doser, so being able to monitor your dose and shots with a full knowledge of dosing is really important.
I've also found that it's fairly easy to start updosing with an e-doser, too, if you don't monitor it enough.
When dialing in espresso, this is my methodology — adjust grind, and then weigh dose and adjust from there. Generally, I've found that a short, finer grind adjustment, complete with the lower dose that follows, will get you a shot that runs just about the same time. So if you start with a 20second, 1.75oz, 20g espresso, moving it finer will give you closer to a 20second, 1.75oz, 18-19g espresso.
Adjusting the dose with the grind is antithetical to the scientific method. You don't want to play with too many variables at the same time.
And like manual dosing, it'll only cut down on waste if baristas are trained properly to do so.