These ergo bar ends are essentially budget copies of Cane Creek's excellent Ergo Controls. Like them, they're made of a firm rubber outer over an aluminium and resin core. They clamp over the bars to form a T-bar grip, and their flowing, curvy shape is easy on your hands.
Having your hands roughly parallel to the direction of travel is much more comfortable, as Dutch roadsters and British touring bikes prove, and so it is here. If you could only access the brakes and gears, it would be tempting to rest your hands on them all the time.
In part, it's the shape and road buzz-free non-metal outer; mostly it's the fact that it's just a better orientation for your hands. Grip is good too. Hillclimbing or acceleration out of the saddle is much easier on your arms; you can bring your shoulders and upper body into play without wrenching your wrists. Unlike most bar ends, these don't mess with your reach either.
Frankly, every flat or riser bar bike should have a pair of these, or the Cane Creeks. The latter are nicer, but these aren't half bad; they live permanently on my hack bike.