I guess they're designed to be marathon racing flats for non-elite runners, so for me at 42, 180# and insanely high arches, Boston 3 would be good for tempos and races, but probably not all my longer runs.
My last injury a couple months ago was from doing a fartlek in my Adidas Aegis flats when my calves were tight. Lack of cushioning, cold temperatures that day lead to straining my left calf. So maybe the Boston 3 would be better for that.
What pisses me off is none of the shoe companies seem to offer a full detailed profile or a chart of what the shoes are meant for, and changes from previous models. For example, I've had a pair of adizero Mana for several years that I don't use often, just for short fast track workouts. They're 7.7 oz. But if I were to replace them, I wouldn't know what to get, because now the Mana is a completely different shoe, with a lot more cushioning, at 9.1 oz.