The USWE packs are excellent. I use one for gravel racing (5-6 hours, typically) as well as 3hr+ local rides on my gravel bike or MTB. My typical setup is high-carb mix in my bottles and plain water in the hydro pack. This has proven to work really well for me, along with other snacks. I haven't used mine on the road, but I could certainly see doing it for a sportive/fondo type event.

As for being more aero, that's still a maybe. Dylan Johnson (gravel pro and marginal gains freak) wind tunnel test found the USWE pack more aero than nothing. Ben Delaney (YouTube gear reviewer and amateur gravel racer) did not get the same results in his wind tunnel test of the same pack.