Nifty 'divot' for the heel of your hand when on the hoods.

Narrow bars (40cm) have less of a flat top, which is over rated anyway.

Mostly you grip the bar tops when climbing, & so don't put much weight so comfort is not an issue.

Aero? I guess. Mainly they look cool & fast.

No tape on the tops makes IAB position sketchy but the internal cable routing is good, once set up.

There's enough round bar at the stem to mount stuff, unlike many of the newer, cooler looking styles.